gdb/testsuite/

gdb/testsuite/
	* gdb.base/break-interp.exp: Remove $exec.debug safety removal.
	* gdb.base/sepdebug.exp: Remove .debug subdirectory handling.  New
	variable different_dir. Move debugfile into a full directory pathname
	under DIFFERENT_DIR.
	* lib/gdb.exp (separate_debug_filename): Remove.
	(gdb_gnu_strip_debug): No longer call separate_debug_filename.  Remove
	variable debug_dir and mkdir of it.  Update function comments.