- fix unterminated string in .IP macro
- fix .TH date format
- properly break line after .PP
- replace .br in table (unsupported by FreeBSD 12's mandoc)

FreeBSD Bug#241032 reported by Helge Oldach

Let the system allocate realpath() buffers intead
of trying to portably derive a buffer size.

This was found with default GCC fortify settings on
Ubuntu 18.04 and showed with -D_FORTIFY_SOURCE=2 on Fedora, too.

dist-tools/makerelease.pl looks for lines matching ^fetchmail- to extract
from NEWS, so make fetchmail 6.4.0 not match that regex.

The fix between 6.4.0-rc4 and 6.4.0 for Debian Bug#941129 caused
a regression in the default file locations, some files were looked
for without dot (.fetchmail.pid, .fetchmailrc).

Reported by Cy Schubert.

This entails recording new line numbers in po/*.po files.

If FETCHMAILHOME is specified as relative path, then it can become
the victim of a chdir("/") that happens in daemon mode, so that
switching to daemon mode will change behaviour of FETCHMAILHOME.

Reported by Alex Andreotti, Debian Bug #941129.

- add copyright notice and license
- add a terse documentation as header
- add an option -n (dry-run) that only prints what would be done.