Merge branch 'jk/diagnose-config-mmap-failure' into maint

The configuration reader/writer uses mmap(2) interface to access the files; when we find a directory, it barfed with "Out of memory?". * jk/diagnose-config-mmap-failure: xmmap(): drop "Out of memory?" config.c: rewrite ENODEV into EISDIR when mmap fails config.c: avoid xmmap error messages config.c: fix mmap leak when writing config read-cache.c: drop PROT_WRITE from mmap of index