Previously we would cut off the source file buffer at the code-completion
point; this impeded code-completion inside C++ inline methods and,
recently, with buffering ObjC methods.
Have the code-completion inserted into the source buffer so that it can
be buffered along with a method body. When we actually hit the code-completion
point the cut-off lexing or parsing.
Fixes rdar://10056932&8319466
llvm-svn: 139086