A couple of kdesrc-build changes:

* kdesrc-build no longer prepends entries to the path that it normally would (such as
$KDEDIR/bin, $QTDIR/bin) if it finds that those entries already exist in the system's
environment variable. (This affects PATH, LD_LIBRARY_PATH, and PKG_CONFIG_PATH for the
most part). The reasoning is that we always want system path entries to be the
least-preferred, so promoting them to near the beginning of the environment variable
inadevertently could have the ill effect of mixing system resources with what we're
trying to build. This was noticed by Jeremy Whiting who is using a system Qt (in /usr)
and had to hack around kdesrc-build to make it work.

* The 'binpath' setting in its first incarnation simply set PATH directly to that value,
so that the then-kdecvs-build could work fine from cron. It later took on a
default value of $PATH, for ease of interactive use, and even later
kdesrc-build changed the way we construct environment variables, so that now
it is PATH=$binpath:$implicitly_set_vars:$PATH. But binpath itself contains
$PATH, which makes this incorrect. Now binpath defaults to nothing, which
should help ensure a correct build, and setting binpath simply prepends those entries
to the front of PATH without clearing the ones already set. (If you need to actually
clear entries, you'll need to do so at the shell or use some kind of wrapper script).