Provide last_hash value as __MKIT_PROJ_GIT_LASTHASH__ token

Note that similar to __MKIT_PROJ_VERSION__, this value cannot be
reliably determined when outside git (e.g. distributor's build dir),
therefore must be kept inside dist source package.

Unlike version, though, user (ie. app developer, ie. mkit.ini
maintainer) most probably does not want to edit it, therefore we're
normally keeping it out of sight.

The value itself is normally just the last git commit's hash (SHA1 these
days), suffixed with ".dirty" mark if there were uncommitted changes
during build.  (Just the same as we do with semver())

If we're outside git and the hash could not be determined, that either
means the source package was mangled with or was built with older
version of mkit.  In either case, the value provided will be 'UNKNOWN'.

src/include/build.sh

         echo "s|__MKIT_PROJ_CODENAME__|$(ini 1value project:codename)|g;"
         echo "s|__MKIT_PROJ_PKGNAME__|$(ini 1value project:pkgname)|g;"
         echo "s|__MKIT_PROJ_TAGLINE__|$(ini 1value project:tagline)|g;"
+        echo "s|__MKIT_PROJ_GIT_LASTHASH__|$(git_lasthash)|g;"
         echo "s|__MKIT_PROJ_VERSION__|$(semver)|g;"
         echo "s|__MKIT_SELF_VERSION__|$MKIT_VERSION|g;"
     } >> "$script"
     #       rpmstuff, hence -f hack for gzip
     #
     local version=$(semver)
+    local git_lasthash=$(git_lasthash)
     local dirname=$MKIT_PROJ_PKGNAME-$version
     mkdir -p "$dirname"
     ini values "lists:dist" | xargs -I DIST_ITEM cp -R DIST_ITEM "$dirname"
     update_version "$version" "$dirname/mkit.ini"
+    mkdir -p "$dirname/.mkit"
+    echo -n "$git_lasthash" > "$dirname/.mkit/git_lasthash"
     tar -cf "$dirname.tar" "$dirname"
     gzip -f "$dirname.tar"      # see above FIXME
     mkdir -p "$MKIT_LOCAL"

src/include/facts.sh

     sed s/^/v/
 }
 
+git_lasthash() {
+    #
+    # Show last commit hash (with .dirty suffix if needed)
+    #
+    # If outside git repo, get it from .mkit/git_lasthash, which
+    # should have been put there by dist target.  (I.e., this won't
+    # work if you got outside the git repo in other way than dist
+    # target, but that's actually expected.)
+    #
+    if git_present;
+    then    # we are in git repo
+        local last_hash=$(git rev-parse HEAD)
+        if test "$(git diff --shortstat 2>/dev/null)" != "";
+        then    # the tree is "dirty", i.e. has been edited
+            local suffix=.dirty
+        fi
+        local suffix=""
+        echo -n "$last_hash$suffix"
+    else    # we are outside (eg. distributor's build dir')
+        grep . .mkit/git_lasthash || {
+            echo UNKNOWN
+            warn "malformed source, could not determine git hash"
+        }
+    fi
+}
+
 semver() {
     #
     # Build semver version string with build metadata