the energy was not correctly updated if the move was accepted

- matheval not needed
- fftw is already on by default

I tested by changing --print-prog-name to --print-prog-namex (not existing) so as to reproduce
the bug, and this seems to fix it so I merge it.

Can be used for numeric comparisons in precompiler directives

Error is this one:
../maketools/makelinks.sh: line 24: echo: write error: Broken pipe

It's triggered by the comparison with a <(echo) file, since the comparison
might fail before echo completes. If this works I will backport it

See #524

thanks to @IsabellGrothaus

This is a harmless mistake, I found it while implementing #653 so I backported the fix

cc: @valsson

This is an issue identified while implementing #653

It is not strictly necessary for PLUMED < 2.8, but I backported
it anyway for clarity and to avoid issue when people copy patches
from one version to another

See failures while testing #687

This reverts commit 3c316e1c.

See failures while testing #687

(cherry picked from commit 66363a3f)