Solution folders are supported as read-only in the VS11 Express
Edition, so do not prohibit their use just because we detect the
express edition (as we did in the VS10 generator).
Inspired-by: Paris
Since the parent commit the local generator Version ivar may be
compared for ordering. Convert comparisons:
"==VS10" becomes ">=VS10"
"!=VS10" becomes "< VS10"
to support an explicit enumeration value for VS11 with no change
in behavior.