Fix a bunch of small system/core bugs.

Missing frees in:
  adb/file_sync_client.c
  fastboot/fastboot.c
  libsparse/output_file.c

Missing closedirs in:
  adb/file_sync_service.c
  cpio/mkbootfs.c
  libcutils/dir_hash.c

Potential buffer overrun in:
  gpttool/gpttool.c

Incorrect NULL check in:
  libsparse/backed_block.c

Bug: https://code.google.com/p/android/issues/detail?id=61564
Change-Id: If97838a9e73a77aef7f416c31c237ce1fca4ce21
restorecon_recursive("/sys") speed boot time

Currently, the restorecon_recursive("/sys") call in
init.c takes approx 2 seconds on hammerhead. This change
reduces the delay to 1.2 seconds.

1) Avoid double stat call when using nftw (time savings
of 0.3 seconds)
2) Avoid the repeated calls to is_selinux_enabled() (time
savings of 0.5 seconds)

Avoid calling lsetfilecon if the file is already properly
labeled. This doesn't speed up the restorecon on /sys,
but it should help when handling files on /data.

Change-Id: Icf344edc5bfc9520d3a0ebd9527a065d29832f87