vmem: modify vmem benchmark, modify makefiles

The mt benchmark has been renamed to vmem_mt. The possibility of creating
pools in a directory has been added. Slight modifications to Makefiles.
Small vmem_valgrind test changes.
vmem: fix possible valgrind test match errors and valgrind version check
Merge pull request #20 from tomaszkapela/VMEM-benchmark-modification

vmem: modify vmem benchmark, modify makefiles