lib/download.c: add basic support for vcdiffs
lib/download.c: use tempfile while decoding new file from binary diff.

this prevents corrupted files when filename == basefile.
lib/download.c: debug output for binary diffs
bin/xbps-uhelper: fix flags for xfetch
lib/download.c: delete vcdiffs after applying; cleanups.
lib/repo_sync.c: use xbps_fetch_delta instead of xbps_fetch_file
xbps-uchroot(8): do not remount / unnecessarily.
bin/xbps-uhelper/main.c: fetch accepts >=2 arguments, not only 2 arguments
bin/xbps-uhelper/main.c: fix english. It's 'identical to' not 'identical than'
NEWS: announce xdelta support
Merge pull request #52 from Gottox/xdelta

support for fetching file deltas for repo_sync.
xbps.h: bump XBPS_API_VERSION.
lib/download.c: style twerks.
NEWS: improve xdelta entry.
lib/download.c: unconstify to fix a warning.
xbps_get_pkg_plist_from_binpkg: fix a double free, found by Gottox.

xbps-query -Rf foo without network was enough to trigger it.
NEWS: tyops
xbps-query(8): added --fulldeptree to print a full dependency tree with -x.

This fixes the regression introduced in 0.37 with -xx; -xx is not supported
anymore, use `--fulldeptree -x`.
xbps-query: fix an obvious tyop that broke -RX.
xbps-install.8: clarify -ff behaviour.