[RTL]

[RTL]
- Post-r52687 implementation of RtlIsDosDeviceName_U is more advanced than pre-r52687 one and covers more corner cases which may not be tested by existing winetests.
- Thus bring back the post-r52687 and also introduce fixes for the following bugs in it:
* Incorrect extension/space-at-the-end truncation
* Incorrect encoding of returned offset/length pair
* Incorrect condition for for-loop exit
* Incorrect calculation of the return length in case of COMx/AUX devices (it should not include the terminating 0 character)
- After those trivial fixes (mostly oneliners and typos), the function works as expected and passes all ntdll_winetest path tests. Sorry for any inconviniences!

svn path=/trunk/; revision=54018