Minor fixes.

1. This is a @Deprecated method and very meaningless to modify, but I changed internal cast of Collection.multiply(Number) from List to Collection. This was a bug.
2. Removed meaningless @SupressWarning of Collection.grep().
3. << to &lt;&lt; in JavaDoc.
4. Fixed some wrong JavaDoc.
GROOVY-6961: fix wrong generics type extraction for extension methods by using the custom declared class instead of backing node
Merge pull request #489 from yukoba/MinorFix

Minor fixes
Introduce a BytecodeDumper class for reuse in tests
GROOVY-6968: Improvements to @ASTTest
remove the mention of the Groovy version
Fixed bug GROOVY-6778

The string "-d" is being used to escape dashes. Thus, converting all dashes to "-d" must be the first replacement that is done (it was) and converting them back must be the last (it wasn't). The bug resulted in the following erroneous conversion:

"-n" -> "-dn" -> "-n" -> "?"
GROOVY-6836: If joint compilation is active *and* that @CompileStatic is used with @Immutable, metaclasses are mixed
groovy-ant part of PR#456
GROOVY-6969: Set.flatten() should return Set
Merge pull request #493 from yukoba/SetFlatten

GROOVY-6969: Set.flatten() should return Set
GROOVY-6970: Type checker should be able to choose between two equivalent interface methods
GROOVY-6849: In case of ambiguity, type checker should be able to choose between an extension method and an interface method
Added missing documentation to BenchmarkInterceptor.java
Added javadoc comments to several Meta* classes
Fixed compilation warnings for javadoc
GROOVY-6971: try to improve performance of GeneratedMetaMethod.Proxy#proxy()
change condition mistake
GROOVY-6952: Add List.removeAt(int) and Collection.removeElement(Object), because for List<Integer>, List.remove(int) and Collection.remove(Object) are troublemakers.