Using xtc-grps with a subset leaks memory
Each XTC-writing step leaks a temporary rvec array of size natoms-xtc-grps.
This affects 4.6.x and 5.0-beta. Uploaded fix will apply to master branch. Will backport to 4.6 later.
Fix, simplify and test XTC writing
The old implementation had various sins, including repeating setup and
leaking natoms_xtc rvecs of memory per step writing xtc-grps when they
are a subset of the whole system. Cleaned lots of things up.
Added integration-style tests for XTC writing.
Added more grompp -n support to integration-style tests, though not
all of it is actually used by this patch.
Also added a pragma to work around a curious warning by ICC 12 on