<rdar://problem/13365424>

Ensure that option -Y also works for expression as it does for frame variable
Also, if the user passes an explicit format specifier when printing a variable, override the summary's decision to hide the value.

This is required for scenarios like this to work:
(lldb) p/x c
(Class) $0 = 0x0000000100adb7f8 NSObject

Previously this would say:
(lldb) p/x c
(Class) $0 = NSObject

ignoring the explicit format specifier

llvm-svn: 177893