* main.c (source_command): Require an explicit pathname of file

	* main.c (source_command):  Require an explicit pathname of file
	to source, since previous behavior of defaulting to gdb init file
	was troublesome and undocumented.
	* printcmd.c (disassemble_command):  Add missing '{}' pair to
	else with two statements.  Bug reported by Stephane Tsacas
	<slt@isoft.fr>.
	* symtab.c (find_pc_line):  Don't complain about zero length or
	negative length line numbers for the moment, since we may not own
	the terminal when called, such as when single stepping.  (FIXME)
	* language.h (CAST_IS_CONVERSION):  True if current language is
	C++ as well as C.  Fix from Peter Schauer.
	* environ.c (get_in_environ, set_in_environ, unset_in_environ):
	Use STREQN macro rather than bare '!strncmp()'.
	* environ.c (unset_in_environ):  Avoid use of memcpy on
	overlapping memory regions, as suggested by Paul Eggert
	<eggert@twinsun.com>.
	* c-exp.y (%union struct):  Remove unused ulval as suggested
	by Paul Eggert <eggert@twinsun.com>.