* gfortran.h: Add flag_backslash compile-time option.
	* lang.opt: Add support for -fbackslash option.
	* options.c: Likewise.
	* primary.c: Implement behavior for -fno-backslash.
	* invoke.texi: Add doc for -fbackslash option.
	* gfortran.texi: Remove mention of -fno-backslash as a
	possible extension.
	* gfortran.dg/backslash_1.f90: New test.
	* gfortran.dg/backslash_2.f90: New test.

From-SVN: r101216