Add support for LEB128 encoded integers (both signed and unsigned). This

Add support for LEB128 encoded integers (both signed and unsigned).  This
is needed for the GAS .uleb128 and .sleb128 directives.

* intnum.c (yasm_intnum_sign): New signedness discovery function.
* intnum.h (yasm_intnum_sign): Prototype.

* intnum.c (yasm_intnum_get_leb128, yasm_intnum_size_leb128): New.
* intnum.h (yasm_intnum_get_leb128, yasm_intnum_size_leb128): Prototype.
* leb128_test.c: New test for intnum-level LEB128 functions.

* bytecode.c (bytecode_leb128): New bytecode and supporting functions.
(yasm_bc_create_leb128): New creation function.
* bytecode.h (yasm_bc_create_leb128): Prototype.

* gas-token.re: Recognize .uleb128 and .sleb128.
* gas-bison.y: Ditto.
(gas_define_leb128): New.
* leb128.asm: New test for GAS .uleb128 and .sleb128 directives.

svn path=/trunk/yasm/; revision=1287