Bump default scala platform version to 2.11

- Change default platform version to `2.11.x`, which has been the recommended major version for about a year.
- Bump patch versions for built in platforms to latest.
- Downgrade the pantsbuild/pants repo to `2.10` in order to upgrade that separately.

Testing Done:
https://travis-ci.org/pantsbuild/pants/builds/162055117

Bugs closed: 3897

Reviewed at https://rbcommons.com/s/twitter/r/4256/

pants.ini

@@ -148,6 +148,8 @@ skip: True
 [pycheck-context-manager]
 skip: True
 
+[scala-platform]
+version: 2.10
 
 [compile.zinc]
 jvm_options: [

src/python/pants/backend/jvm/subsystems/scala_platform.py

@@ -25,11 +25,11 @@
 scala_build_info = {
   '2.10':
     major_version_info(
-      full_version='2.10.4',
+      full_version='2.10.6',
       style_version='0.3.2'),
   '2.11':
     major_version_info(
-      full_version='2.11.7',
+      full_version='2.11.8',
       style_version='0.8.0'),
 }
 
@@ -92,14 +92,16 @@ def register_style_tool(version):
                             classpath=[jardep])
 
     super(ScalaPlatform, cls).register_options(register)
-    register('--version', advanced=True, default='2.10',
+    register('--version', advanced=True, default='2.11',
              choices=['2.10', '2.11', 'custom'], fingerprint=True,
              help='The scala platform version. If --version=custom, the targets '
                   '//:scala-library, //:scalac, //:scala-repl and //:scalastyle will be used, '
                   'and must exist.  Otherwise, defaults for the specified version will be used.')
 
     register('--suffix-version', advanced=True, default=None,
-             help='Scala suffix to be used when a custom version is specified.  For example 2.10.')
+             help='Scala suffix to be used in `scala_jar` definitions. For example, specifying '
+                  '`2.11` or `2.12.0-RC1` would cause `scala_jar` lookups for artifacts with '
+                  'those suffixes.')
 
     # Register the fixed version tools.
     register_scala_compiler_tool('2.10')