Attempt to genericise the location type, by replacing
"type location = ..." in location.ml with just "type location". This
doesn't really work, because the other tools in the diy suite assume
that the Location_reg and Location_global constructors of the location
type are made public. So, in my next commit, I will rollback and
try a different approach.
Revert "Attempt to genericise the location type, by replacing"

This reverts commit 65b694b67f7450f1ff1a2e9b6b862cbad9a68935.
Added ability to refer to "the set of events that access a
global location" and "the set of events that access a local
location" in OpenCL cat files. To enable this, one should insert
a line like "x : local, y : global" into each OpenCL litmus
test.