[analyzer] Specialize "loop executed 0 times" for for-in and for-range loops.

The path note that says "Loop body executed 0 times" has been changed to
"Loop body skipped when range is empty" for C++11 for-range loops, and to
"Loop body skipped when collection is empty" for Objective-C for-in loops.

Part of <rdar://problem/14992886>

llvm-svn: 194234