* config/tc-mips.c: Add define for $zero register.

	* config/tc-mips.c: Add define for $zero register.
	(md_begin): Add $zero as alias name for $0.
	(insn_uses_reg): Use ZERO define.
	(mips_ip): Add $zero as alias name for $0.
	(mips16_ip): Likewise.
	(s_cplocal): Demand empty rest of input line.
	(tc_get_register): Likewise. Add support for $kt0, kt1 register
	names. Use ZERO define. Fix input_line_pointer progress.