@giovannibussi right?

- dumpgrid
- pca
- mds

LDFLAGS were overwritten by mistake by CFLAGS when doing coverage

this makes the link visible also when browsing with a mobile

Closes #354

opMap is now constructed in a single statement. This avoids
problems possibly arising with multiple threads accessing for the first time
to this method simultaneously.

opMap is then made const for clarity.

(cherry picked from commit 10cbe7e8)

Fix for bug in TD_GRID

Fixed typo in grid spacing lookup

See merge request MPIP-Valsson-Group/plumed2-ves!4