Fix handling of memory usage in KLEE.

Memory usage API in LLVM since 3.3 is not working the way it is
intended by KLEE. This ports the pre 3.3. version to KLEE.

Fixes the malloc test case.
Have configure check for presense of mallinfo for the newly added
klee::util::GetTotalMemoryUsage()
Modify klee::util::GetTotalMemoryUsage() so that if the system is
not using glibc the malloc usage if computed differently.
Renamed GetTotalMemoryUsage to GetTotalMallocUsage
Merge pull request #116 from MartinNowack/fix_malloc

Fix handling of memory usage in KLEE.