Added two targets acquire-localbase-lock and release-localbase-lock,
which mark the complete LOCALBASE directory as locked, so that multiple
packages cannot run the install, deinstall or bin-install targets at the
same time.
The install target aquires locks in both WRKSRC and LOCALBASE, the other
two targets only need the LOCALBASE lock, since they may be run without
WRKSRC being present on the system.
locking.mk must be included before tools.mk and the PKG_FAIL_REASON
check.
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