This micro-optimizes again the implementation of a couple of hot functions
after recent changes.  No functional changes.

Tested on x86_64-pc-linux-gnu, committed on trunk

2017-04-25  Eric Botcazou  <ebotcazou@adacore.com>

	* fname.adb (Has_Internal_Extension): Add pragma Inline.
	Use direct 4-character slice comparisons.
	(Has_Prefix): Add
	pragma Inline.	(Has_Suffix): Delete.
	(Is_Internal_File_Name):
	Test Is_Predefined_File_Name first.
	(Is_Predefined_File_Name):
	Use direct slice comparisons as much as possible and limit all
	comparisons to at most 8 characters.