Don't use hexadecimal "timestamps"

Hexadecimals were used to save few characters, but it turns out that
while lexical sort should be fine, in version modes they do tend to
sort in strange ways (eg. `t5af5e80a < t5af5e800` in rpm).

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 btime         # 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' "$(date +%s)") ;;
+        btime)  btime=$(date -u +%Y%m%d%H%M%S) ;;
     esac
     grep ":" <<<"$prerl" \
      && warn "colon in project:prerl may corrupt version data: $prerl"

src/include/vars.sh.skel

 #
 # 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).
+# If 'btime', devel builds have also timestamp-based tag in format of
+# `t%Y%m%d%H%M%S`, that is, a small character 't' followed by timestamp
+# without non-digit characters.  The timestamps are in UTC, ie. timezones
+# need not apply.
+#
+# This helps with deploying development builds where packaging system
+# is not SemVer-compliant and makes it hard to install arbitrary version.
+# For example, old yum version (as of RHEL-6) will not let you install
+# version that it deems older than is installed, making it hard to
+# continually upgrade during active development.  While packaging
+# systems have their own rukes (and SemVer says both versions should be
+# considered same) this tag will make it more likely to "win" the build
+# you made later.
 #
 # Note that this makes devel and dirty builds non-deterministic,
 # but does not affect clean builds (ie. builds from clean repo