improve detecting PATH= without $PATH, update #1785
NEXT: [GH-1786] for 1.19.2
fix rvm_autolibs_flag in __rvm_parse_args_find_known_flags, update #1785
NEXT: [GH-1785] for 1.19.2
fix detecting not writable cellar in homebrew, fix #1785
NEXT: [GH-1785] for 1.19.2
use rubygems --verbose installation only when --debug or --trace, closes #1772
NEXT: [GH-1772] for 1.19.2
fix 16405e8, update #1772
NEXT: [GH-1772] for 1.19.2