Clean up manipulation of chunk page map elements to remove some tenuous

Clean up manipulation of chunk page map elements to remove some tenuous
assumptions about whether bits are set at various times.  This makes
adding other flags safe.

Reorganize functions in order to inline i{m,c,p,s,re}alloc().  This
allows the entire fast-path call chains for malloc() and free() to be
inlined. [1]

Suggested by:	[1] Stuart Parmenter <stuart@mozilla.com>