Refactoring of Get() methods in FormatManager/FormatCategory to have...

Refactoring of Get() methods in FormatManager/FormatCategory to have explicative names and return shared-pointers instead of bools
Reduced the amount of memory required to avoid loops in DumpPrintableRepresentation() from 32 bits down to 1 bit
 - Additionally, disallowed creating summary strings of the form ${var%S} which did nothing but cause endless loops by definition

llvm-svn: 139201