Having FileManager::getFile always open the file, brought much consternation...

Having FileManager::getFile always open the file, brought much consternation and leaking of file descriptors.

Add 'openFile' bool to FileManager::getFile to specify whether we want to have the file opened or not, have it
false by default, and enable it only in HeaderSearch.cpp where the open+fstat optimization matters.

Fixes rdar://9139899.

llvm-svn: 127748