Bump version number to 0.5.4 and write History.md.
find_mongo_pids: Fix regression in 203a82d.

Don't consider "ps" stderr to be an error. This occurs on OSX Mountain Lion if
DYLD_LIBRARY_PATH or a similar env var is set, and is harmless.
Merge branch 'release-0.5.4'
Merge branch 'master' into devel