* defs.h (QUIT): Call interactive_hook to allow GUI to interrupt.

	* defs.h (QUIT):  Call interactive_hook to allow GUI to interrupt.
	Also, add decl for symtab_to_filename.
	* gdbtk.c:  Replace calls to full_filename with symtab_to_filename.
	* gdbtk.tcl:  New routine pc_to_line replaces in line code.  New
	routine decr replaces in line code.
	* (create_file_win):  Use catch to handle open failures more
	elegantly.  Also, create special window to display file open
	failure message.  Move opening of file prior to creation of text
	widget.
	* (create_asm_win):  Add PC as argument.  We now base disassembly
	on PC instead of function name, since function names can be
	ambiguous (usually seen with shared libs).  Also, use catch to
	simplify code where we don't care about failures.
	* source.c (symtab_to_filename):  New.  Returns the file
	associated with a symtab.
	* top.c:  Define interactive_hook.  Called during QUIT to animate
	the GUI.