Create a temporary directory for use during testing
Updating scripts to use CHPL_TEST_TMP_DIR
Making mktemp compatible with linux and osx; Adding -f to rm of temp dir
Merge pull request #237 from benharsh/fasta-stdin-perf

CHPL_TEST_TMP_DIR, if not specified, will point to a mktemp'd directory for use during testing. It is removed at the end of every test.

Also updated are the fasta-dependent performances scripts that generate files, where the target is now this new temporary directory.