Revision 1887060

Align apr_mmap()ing offset to a page boundary.  PR 65158.

This is requirement for unix systems, and otherwise can cause failures or
undefined behaviour with some filesystems.

Add apr_mmap_t->poffset on unixes to track the offset to the previous page,
relative to the user requested/actual offset. This allows ->mm and ->size to
still point to the actual data, while munmap() now deletes the full range
from the start of the page.

Tests updated accordingly.