An argument in the form gem:ver is pull apart into the gen name and
version, respectively.
# File lib/rubygems/command.rb, line 192
def get_all_gem_names_and_versions
get_all_gem_names.map do |name|
if /\A(.*):(#{Gem::Requirement::PATTERN_RAW})\z/ =~ name
[$1, $2]
else
[name]
end
end
end