improved alpha channel handling for math ops, removed 'can't substract or divide a color from a number' constraint
Merge branch 'color-ops-fixes' of https://github.com/seven-phases-max/less.js

Conflicts:
	test/less/errors/color-operation-error.txt
add changelog
Merge branch 'master' of https://github.com/cloudhead/less.js
add transparency colour function change to the changelog