Decide whether or not a terminal can be resized.

Decide whether or not a terminal can be resized.

Use resize.bashrc to set the RESIZABLE environment variable.
If RESIZABLE is 0 the current terminal cannot be resized.
If RESIZABLE is the same as TERM in can be resized.
Maintain a list of terminals we know can't be resized, eg sun-color.
Maintain a list of terminals which we can't be sure about, eg screen
since whether or not screen can be resized depends on the (unknown)
capabilities of the underlying terminal.
For any other terminal assume it can be resized.
In vim, set the g:resizable variable based on the value of RESIZABLE
(and set it to 1 in the GUI).  Call Can_Resize() before trying to resize
the window.
Allow setting g:resizable manually to override this logic.