improve resolving scripts path in db
Merge pull request #2149 from wayneeseguin/bugfix/github_issue_2149

rvm db doesn't respect autolibs=read-fail
make sure to use full path when sourcing rvm using relative path
Merge pull request #2150 from wayneeseguin/bugfix/github_issue_2150

sourcing $RVM_PATH/scripts/rvm sets wrong environment variable for rvm_bin_path and rvm_prefix