Bump version to 2.28.51

Bump version to 2.28.51

bfd/
2016-12-23  Tristan Gingold  <gingold@adacore.com>

	* version.m4: Bump version to 2.28.51
	* configure: Regenerate.

binutils/
2016-12-23  Tristan Gingold  <gingold@adacore.com>

	* configure: Regenerate.

gas/
2016-12-23  Tristan Gingold  <gingold@adacore.com>

	* configure: Regenerate.

gprof/
2016-12-23  Tristan Gingold  <gingold@adacore.com>

	* configure: Regenerate.

ld/
2016-12-23  Tristan Gingold  <gingold@adacore.com>

	* configure: Regenerate.

opcodes/
2016-12-23  Tristan Gingold  <gingold@adacore.com>

	* configure: Regenerate.