Add note about dropping support for Python v2.5

After some discussion on the roundup-devel mailing list it was agreed
that support for Python v2.5 should be dropped in the v1.6 release of
Roundup.

Dropping support for Python v2.5 should allow a number of cleanups to
the code base as well a provide and opportunity to start porting Roundup
to Python v3.

Author: jerrykan

CHANGES.txt

@@ -6,6 +6,10 @@ and template changes not listed here.
 Each entry has the developer who committed the change in brackets.
 Entries without name were done by Richard Jones.
 
+**IMPORTANT** The v1.5.x releases of Roundup will be the last to support Python
+v2.5. Support for Python v2.5 will be dropped with the v1.6 release of Roundup,
+at which point users will need to run Roundup using either Python v2.6 or v2.7.
+
 
 2014-??-??: 1.5.1
 

doc/upgrading.txt

@@ -11,6 +11,10 @@ then you don't need to do anything. If you're upgrading from 0.5.6 to
 0.6.8 though, you'll need to check the "0.5 to 0.6" and "0.6.x to 0.6.3"
 steps.
 
+**IMPORTANT** The v1.5.x releases of Roundup will be the last to support Python
+v2.5. Support for Python v2.5 will be dropped with the v1.6 release of Roundup,
+at which point users will need to run Roundup using either Python v2.6 or v2.7.
+
 Contents:
 
 .. contents::