Added support for changing the color mappings. The curses color
for a given host color can be specified with the resource
c3270.cursesColorForHostColorn, where n is a
host color number (0 through 15), and the value of the resource is a
curses color number (0 through 7).
In addition, the field-attribute-based colors used when the host
does not specify a particular color can be changed via the following
resources:
c3270.cursesColorForDefault
c3270.cursesColorForIntensified
c3270.cursesColorForProtected
c3270.cursesColorForProtectedIntensified
The value for each of these is a curses color number (0 through 7).