We recently had issues with definitions of a Bohr not being consistent
between Modules/constants.f90 and PW/tools/pwo2xsf.sh. The pwo2xsf.sh
script used less significant digits, which lead to symmetry breaking
breaking in some cases. This commit uniformizes the definition of a Bohr
across the various PW/tools with the one in Modules/constants.f90 to
avoid such problems.