Add timestamp to dirty and devel builds

Helps ensure that a later devel build will install over older one.

src/include/facts.sh

     local latest_tag    # latest git tag
     local commit        # commit indicator (CURRENT_BRANCH.gHASH)
     local dirty=F       # F if dirty, T if clean
+    local btime         # hex timestamp or nothing (see $MKIT_TTAG)
     local suffix        # version suffix
     prerl=$(ini 1value project:prerl)
+    case $MKIT_TTAG in
+        none)   btime= ;;
+        btime)  btime=$(printf '%08x' "$(date +%s)") ;;
+    esac
     grep ":" <<<"$prerl" \
      && warn "colon in project:prerl may corrupt version data: $prerl"
     git_present || {
         commit="$(git_fact current_branch).g$(git_fact latest_sha)"
     fi
     git_bool dirty && dirty=T
-    case "$dirty:$commit" in
-        F:)  suffix=""               ;;
-        T:)  suffix="+dirty"         ;;
-        F:*) suffix="+$commit"       ;;
-        T:*) suffix="+$commit.dirty" ;;
-        *)   suffix=MKIT_BUG
-             warn "MKIT_BUG: bad dirt/commit detection" ;;
+    case "$dirty:$btime:$commit" in
+        F:*:)   suffix=""                       ;;
+        T::)    suffix="+dirty"                 ;;
+        T:*:)   suffix="+t$btime.dirty"           ;;
+        F::*)   suffix="+$commit"               ;;
+        F:*:*)  suffix="+t$btime.$commit"         ;;
+        T::*)   suffix="+$commit.dirty"         ;;
+        T:*:*)  suffix="+t$btime.$commit.dirty"   ;;
+        *)      suffix=MKIT_BUG
+                warn "MKIT_BUG: bad dirt/commit detection" ;;
     esac
     test -n "$prerl" && suffix="-$prerl$suffix"
     echo "$xyz$suffix"

src/include/vars.sh.skel

 #
 MKIT_PROJ_PKGNAME=""
 
+#
+# Add time-based ordinal tag to SemVer build data?
+#
+# Can be 'none' or 'btime'.
+#
+# If 'btime', devel builds have also 'tXXXXXXXX' tag, where each
+# 'X' is a hexa-decimal digit of Unix timestamp taken when build
+# is initiated.  This way, builds from same branch are guarranteed
+# to order based on build time (that is, until February 7th, 2106).
+#
+# Note that this makes devel and dirty builds non-deterministic,
+# but does not affect clean builds (ie. builds from clean repo
+# with HEAD corresponding to latest version tag.).
+#
+MKIT_TTAG=${MKIT_TTAG:-btime}
+
 #
 # This MKit version
 #