Filter redundant/incompatible rvm_gem_options

[felixbuenemann]

This removes any occurrence of --no-document, --no-ri and --no-rdoc from rvm_gem_options when merging with the auto-detected install_params to avoid duplicate, deprecated or incompatible options.

This should fix the current test failures for ruby-1.8.7 under Xenial on Travis CI, where the default Travis ~/.rvmrc contains rvm_gem_options='--no-ri --no-rdoc --no-document' breaking rvm gem installs with rubygems 1.8.25 which does not yet support the --no-document option.

[felixbuenemann]

While it would be possible to fix the rvm CI failures simply by patching the existing ~/.rvmrc, I chose to fix this in rvm instead, since it's likely to help other rvm users.

The regex is fairly defensive, to guard against things like --no-rdoc-foo, but has no guards at the beginning of the string due to weird differences in how BSD and GNU sed handle matching. However unless some gem requires an absurd flag like --not-posix-style--no-document that shouldn't really be a problem.

A valid case that we wouldn't catch is rvm_gem_options with embedded quoting around params:

rvm_gem_options='"--no-rdoc" "--no-ri"'

That's agaib pretty unlikely to be used in rvmrc and IMHO not worth the trouble (especially given the limitations and portability of sed's extended REs).

[felixbuenemann]

The remaining test failure is fixed by #4704.

[pkuczynski]

Good work, thanks!