Fix native code uneffective loads after recompilation

Fix native code uneffective loads after recompilation

'dlopen' can return the same handle if two shared with the same
filename are loaded in two different times (even if the first was
deleted!).  To prevent this scenario the last modification time of the
source file is included in the hashing algorithm.

	* src/comp.c (Fcomp_el_to_eln_filename): Update hashing algo to
	include the source last modification date.
	* src/lread.c (maybe_swap_for_eln): Do not check for eln newer
	then elc as this is now unnecessary.