Performs various checks before installing the gem such as the install repository is writable and its directories exist, required Ruby and rubygems versions are met and that dependencies are installed.
Version and dependency checks are skipped if this install is forced.
The dependent check will be skipped if the install is ignoring dependencies.
Installs from the gem dependencies files in the :gemdeps option in options, yielding to the block as in install.
If :without_groups is given in the options, those groups in the gem dependencies file are not used. See Gem::Installer for other options.