feat: add FORTRANPATH to config

In my non standard setup, I ran into the problem that openloops picked the mod files from an older version, since I had to add -I/usr/include to the f_flags for the oneloop mod files to be found. Instead, adding it to FORTRANPATH is better as possible with the patch given below. Further, it includes a change to OLLibrary.py such that a user provided FORTRANPATH is always the last, since the newly compiled mod files should take precedence over existing mod files.

diff --git i/SConstruct w/SConstruct
index 974026e..1bf68b2 100644
--- i/SConstruct
+++ w/SConstruct
@@ -387,6 +387,8 @@ env = Environment(tools = ['default', 'textfile'] + [config['fortran_tool']],
                   FORTRANFLAGS = config['f77_flags'] + config['generic_optimisation'],
                   F90FLAGS = config['f90_flags'] + config['generic_optimisation'],
                   LINKFLAGS = config['link_flags'],
+                  FORTRANPATH = config['f77_path'],
+                  F90PATH = config['f90_path'],
                   LIBPATH = [config['generic_lib_dir']],
                   DOLLAR = '\\$$',
                   RPATH = [HashableLiteral('\\$$ORIGIN')],
diff --git i/pyol/config/default.cfg w/pyol/config/default.cfg
index ed2a5a5..78917ad 100644
--- i/pyol/config/default.cfg
+++ w/pyol/config/default.cfg
@@ -126,6 +126,9 @@ link_flags = %(common_flags)s
 # common Fortran compiler options, added to f77_flags and f90_flags
 f_flags = %%(%(fortran_tool)s_f_flags)s %(common_flags)s
 noautomatic = %%(%(fortran_tool)s_noautomatic)s
+f77_path = 
+f90_path = 
+f_path = 
 
 import_env = PATH LD_LIBRARY_PATH CPATH C_INCLUDE_PATH CPLUS_INCLUDE_PATH INTEL_LICENSE_FILE
 math_cmd = math
diff --git i/pyol/tools/OLBaseConfig.py w/pyol/tools/OLBaseConfig.py
index 4461a9e..6e996a0 100644
--- i/pyol/tools/OLBaseConfig.py
+++ w/pyol/tools/OLBaseConfig.py
@@ -184,6 +184,9 @@ def get_config(args=[]):
     parse_option(config, 'f77_flags', interpolate=True, converter=split_list)
     parse_option(config, 'f90_flags', interpolate=True, converter=split_list)
     parse_option(config, 'f_flags', interpolate=True, converter=split_list)
+    parse_option(config, 'f77_path', interpolate=True, converter=split_list)
+    parse_option(config, 'f90_path', interpolate=True, converter=split_list)
+    parse_option(config, 'f_path', interpolate=True, converter=split_list)
     parse_option(config, 'common_flags', interpolate=True, converter=split_list)
     parse_option(config, 'link_flags', interpolate=True, converter=str.split)
     parse_option(config, 'debug_flags_1', converter=split_list)
@@ -220,6 +223,8 @@ def get_config(args=[]):
 
     config['f77_flags'] = config['f77_flags'] + config['f_flags']
     config['f90_flags'] = config['f90_flags'] + config['f_flags']
+    config['f77_path'] = config['f77_path'] + config['f_path']
+    config['f90_path'] = config['f90_path'] + config['f_path']
     config['link_flags'] = config['link_flags'] + config['link_optimisation']
 
     config['compile_libraries'].extend(['olcommon', 'openloops', 'trred'])
diff --git i/pyol/tools/OLLibrary.py w/pyol/tools/OLLibrary.py
index 43b6804..2fda89d 100644
--- i/pyol/tools/OLLibrary.py
+++ w/pyol/tools/OLLibrary.py
@@ -164,10 +164,10 @@ class OLLibrary:
             f_path = [f_path]
         if isinstance(f90_path, strtype):
             f90_path = [f90_path]
-        f_path = f_path + [os.path.join(config['lib_src_dir'], dep, 'mod')
-                           for dep in self.mod_dependencies] + [self.mod_dir]
-        f90_path = f90_path + [os.path.join(config['lib_src_dir'], dep, 'mod')
-                               for dep in self.mod_dependencies] + [self.mod_dir]
+        f_path = [os.path.join(config['lib_src_dir'], dep, 'mod')
+                    for dep in self.mod_dependencies] + [self.mod_dir] + f_path 
+        f90_path = [os.path.join(config['lib_src_dir'], dep, 'mod')
+                    for dep in self.mod_dependencies] + [self.mod_dir] + f90_path
         if self.mod_dir and not os.path.isdir(self.mod_dir):
             os.makedirs(self.mod_dir)