Implement GEM dependency check
Todo is actually already finished :-)
Merge pull request #1241 from bovi/add-gem-dependency-check

[mrbgems] GEM Dependency Check
consider gem version to be 0.0.0 unless specified
consider empty version requirements as >= 0.0.0
fix regexp warning: character class has duplicated range
remove unused variables
Merge pull request #1244 from NARKOZ/regexp-warning

fix regexp warning: character class has duplicated range
Print mrb_value instead of RClass*
Merge pull request #1247 from carsonmcdonald/issue1246fix

Print mrb_value instead of RClass*
Merge pull request #1245 from NARKOZ/fix-warnings

remove unused variables
Merge pull request #1242 from schmurfy/gem_version

consider gem version to be 0.0.0 unless specified
fix indentation
Merge branch 'master' into iij