[NTOS]: Add MiRemoveZeroPageSafe helper function, when a zero page is required, but...

[NTOS]: Add MiRemoveZeroPageSafe helper function, when a zero page is required, but the inline zeroing of MiRemoveZeroPage is not. This function will only try grabbing a zero page if one exists, otherwise a free page will be grabbed and zeroed with custom code of the caller's choosing.
[NTOS]: Add concept of process color and system color. Compute correct color to use whenever requesting a page.
[NTOS]: Uncondtionally enable the color code when inserting/removing pages.
For now, when requesting a page, colors are still ignored, and the global PFN lists are scanned instead. If there are no regressions, we are one patch away from that.

svn path=/trunk/; revision=48927