[PATCH 0 of 3] Case folding changes

[Paul Moore]

This patch series adds support for case folding filesystems. It comes in 3
parts - a dirstate method to check if the working directory is on a
case-folding filesystem, a util function to convert a filename to the case
stored in the filesystem, and a method on the dirstate to "normalize" a
pathname, which is used in the dirstate.statwalk function.

Combined, these patches fix issues 910 and 1092, and implement infrastructure
to allow fixing of further case sensitivity bugs.