making MDS index type and set size user-defined

Adding CMake variables to control MDS_SET_MAX
and the type of mds_id.

Hopefully mds_id was handled carefully enough
that there is no 32-bit bottleneck to fall through,
but it has never been tested past those limits.

MDS_SET_MAX is also something we quadrupled just
for the twisted meshes that Simmetrix makes
for PHASTA. users should be able to choose
how much cobweb they will tolerate.
fix hardcoded int that should be mds_id
fix serious bug in smb match IO

I was using the wrong type enum
for matches, and apparently
Valgrind and friends aren't smart
enough to catch this.
anyway, it should be fine through pure
luck but the cautious should regenerate
their matched meshes.