disc1 make target in src/release used to use a separate REPODIR.
I prefere to 'make packages' in src/ (after compiling world + kernel) and re-use the freshly created packages.
REPODIR can hold more than one set of packages, which this patch takes into account (uses what 'latest' points to only).
This patch also introduces the STAGING_MFSMOUNT make variable in order to move staging directories onto RAMdisk for example.
If defined, WSTAGEDIR, KDTAGEDIR and SSTAGEDIR are created beyond ${STAGING_MFSMOUNT}
mdmfs mdmfs -s 3g md /tmp/stagingmfs-pkgbase; make STAGING_MFSMOUNT=/tmp/stagingmfs-pkgbase packages
PKG_ABI_FILE was adjusted to take vanishing WSTAGEDIR into account.
In addition to the functional extension this patch marks release/disc1 target outdated if scripts/pkgbase-stage.lua fails.
This covers only a small fraction of possible failures, hence still requires the user to issue 'make clean' (in src/release) at own discretion, but in some cases it can prevent force-wasting time.