gdb/

gdb/
	* corefile.c (reopen_exec_file): Only check for an open exec file.
	Use exec_file_attach.
	* exec.c (exec_open): Make static.
	(exec_file_command): Don't use target_preopen.  Query directly about
	changing the file.
	* gdbcore.h (exec_open): Remove prototype.
gdb/testsuite/
	* gdb.base/completion.exp: Update for change in "file" behavior.
	* gdb.stabs/weird.exp: Likewise.
	* lib/mi-support.exp (mi_gdb_file_cmd): Likewise.
	* lib/gdb.exp (gdb_file_cmd): Likewise.  Kill the program explicitly.