util: add an interpolate() function to for replacing multiple values util.interpolate can be used to replace multiple items in a string all at once (and optionally apply a function to the replacement), without worrying about recursing: >>> import util >>> s = '$foo, $spam' >>> util.interpolate(r'\$', { 'foo': 'bar', 'spam': 'eggs' }, s) 'bar, eggs' >>> util.interpolate(r'\$', { 'foo': 'spam', 'spam': 'foo' }, s) 'spam, foo' >>> util.interpolate(r'\$', { 'foo': 'spam', 'spam': 'foo' }, s, lambda s: s.upper()) 'SPAM, FOO' The patch also changes filemerge.py to use this new function.