commands refactoring, wip
Commands refactoring: IsMaster, R/W 2.6 commands
WIP on new generic collections with Commands and 2.6 new R/W ops
Continuing on new generic collections with Commands and 2.6 new R/W ops
New generic collections with Commands and 2.6 new R/W ops: tests ok
GenericCollection: cleanup + write concern API consistency
Remove BufferWriter/BufferReader (useless now)
Replace db/collection commands by the new command framework
FindAndModify
Commands: Error handling. FindAndModify tests. LowLevelDocumentIterator.
exclude mongodb 2.6 specific tests as travis.ci is not up to date yet
Tag batch commands test as mongo-2.6 specific
fix scala 2.10 compilation in tests
DropIndexes command. Deprecate indexmanager.delete in favor of indexmanager.drop + introduce dropAll method
BSON Raw command implementation. Deprecate reactivemongo.core.commands
Deprecate more commands from reactivemongo.core.commands
Merge branch 'commands-refactoring'

Conflicts:
	driver/src/main/scala/api/api.scala
	driver/src/main/scala/api/bulk.scala
	driver/src/main/scala/api/collections/genericcollection.scala
	driver/src/main/scala/core/actors.scala
	driver/src/main/scala/core/commands/commands.scala
	driver/src/test/scala/CommonUseCases.scala
	driver/src/test/scala/IndexesSpec.scala