ITS#7783 workaround stupid NSPR bug

free(NULL) is supposed to be safe. "Portable wrapper libraries"
that fail to preserve this behavior are inherently broken.
But then again, this is Mozilla code, so that's redundant.
Make sure mapsize changes take effect on Windows.
ITS#7778 fix regression from #7329
Revert "ITS#7772 Reduce spurious sub-page growth."

This reverts commit 75494c08b49c3ef77dce8a00f2bc44c83658c1a7,
which must await a fix to ITS#7771 (DUPSORT cursor tracking).
Note changes for LMDB 0.9.11
Merge remote-tracking branch 'origin/mdb.master'
Bump version to 0.9.11
Merge remote-tracking branch 'origin/mdb.master'