When providing code completions of ivar names for a property

implementation such as

  @synthesize Prop1 = 

Give priority to ivars whose type matches or closely matches the
property type (as we do for several other kinds of
results). Additionally, if there is an ivar with the same name as the
property, or differs only due to a _ prefix or suffix, give that ivar
a priority bump. Finally, verify that this search is properly
returning ivars within class extensions and implementations
(<rdar://problem/8488854>).

llvm-svn: 129699