Terminal: Add putty-256color as a VT100 color-capable terminal

Using PuTTY with the terminal type set to putty-256color causes CMake
not to output any colors during build. Changing it to one of the
'supported' terminal types fixes the problem. This patch adds the
putty-256color terminal type to the list of supported terminals.

Change-Id: I0f261017f2a47348306a5c8da3e2c0e2f906c161