make any path check in drcov2lcov case-insensitive on Windows

From zhao...@google.com on May 07, 2014 18:04:47

We have seen the pdb convert paths to all-lowercase, so the any path check should be case-insensitive on Windows. This may need move some code from DR core to drx.

Original issue: http://code.google.com/p/dynamorio/issues/detail?id=1445