skip adding value to variable when prefix is already there, fix #2332
fix snapshot script: __rvm_tar is not a bash variable
Merge pull request #2334 from lamvak/bugfix/__rvm_tar

fix snapshot script: __rvm_tar is not a bash variable
separate CC from initially_selected_compiler, fix #2336
Merge branch 'master' of github.com:wayneeseguin/rvm
fix and add the ssl_no_ec2m.patch for ruby/1.8.7 for centos/fedora/redhat, fix #2343
improve sourcing rvm in zshrc file, update #2338
add name parsing and default CC for clang ruby, fix #2342
move system build configs to separate callbacks
cleaning and reformating build_config