fix order of operations when getting rvm_ruby_string

fixes https://github.com/wayneeseguin/rvm/issues/2529
load project config after sourcing default ruby, fix #2531
safer version lookup

see https://github.com/wayneeseguin/rvm/pull/2530#issuecomment-31909954
Merge pull request #2530 from ghiculescu/master

fix order of operations when getting rvm_ruby_string
extended code to check ruby version for irb, update #2530
speedup extending ruby name in upgrade, update #2517
add deugging information for failed select when expanding ruby names, update #2517
fix endless loop when checking jruby version when checking jruby version, update #2528
fix detecting zsh version that supports chpwd_functions, fix #2515