Implement toSingleBox.

The toSingleBox method takes a List[Box[T]] and turns it into a
Box[List[T]], via an implicit conversion to ListOfBoxes.
Simplify the toSingleBox implementation.
Update toSingleBox doc to state that List sizes may differ.
Merge pull request #1525 from lift/msf_issue_1525

Implement a helper for Iterator[Box[T]] => Box[List[T]]
Add LiftRules.supplementalHeaders and deprecate supplimental variant.

supplementalHeaders is now a FactoryMaker, whereas supplimentalHeaders was a
volatile var containing a generation function, though it had recently been
switched to point to the listOfSupplimentalHeaders FactoryMaker.
Version bump to 2.6-M3 for release.
Version bump to 2.6-SNAPSHOT for forward development.
Build the 2.10 edition of Lift 2.x using Scala 2.10.4
Bump us to sbt 0.13.1.
Liftsh is now smart enough to download the sbt launcher for you.
Ignore the sbt launcher jar under project/
Fix the deprecation warning in jsonCall.

It was referring to JValue=>JValue methods, but should have been referring to
JValue=>JsCmd ones.
Deprecate S.fjsonCall, which does not use lift-json.
Deprecate a bunch of stuff that uses the old JSONParser.
Deprecate jsonFmapFunc with old JSONParser.

Also add non-deprecated equivalents that do JValue=>JsCmd.
Deprecate legacy JSONParser things in MetaRecord.
Add proper deprecation warnings to two methods.

These were deprecated in the scaladoc but not annotated as such, so did not
emit warnings.
Change default scala version to 2.10.4.

The 2.10 compiler is so much quicker that it makes sense for that to be
the default version we're using.
Merge pull request #1545 from lift/scaladoc-deprecations

2.6: Add proper deprecation warnings to two methods.
Deprecate xbind-related things in Mapper.

This includes a bunch of field binding and form snippet
helpers. New versions are added for doing similar things with
CssSels instead.