refactored case-match in ConfigurationParser.getRepositories
Additional options for Ivy resolvers.

Specify an Ivy resolver with ", descriptorOptional" to make Ivy
descriptor files optional for that repository or with
", skipConsistencyCheck" to disable Ivy consistency checks for
that repository.
Add factory methods to PatternsBasedRepository

This commit adds convenience methods to PatternsBasedRepository that
produce a copy of the repository with metadata optional or with
consistency checking disabled.