tweaked build version strings

- added wmakePrintBuild -check, -update, -version options
- only update .build cache when explictly requested and
  from within the wmake Cver rules
- use -check option to avoid unnecessary remake in src/Allwmake

src/Allwmake

@@ -2,8 +2,8 @@
 cd ${0%/*} || exit 1    # run from this directory
 set -x
 
-# force update of Foam::FOAMversion string (git tag or $WM_PROJECT_VERSION)
-/bin/rm -f OpenFOAM/Make/$WM_OPTIONS/global.? 2>/dev/null
+# update Foam::FOAMversion string if required
+wmakePrintBuild -check || /bin/rm -f OpenFOAM/Make/$WM_OPTIONS/global.? 2>/dev/null
 
 wmakeLnInclude -f OpenFOAM
 wmakeLnInclude -f OSspecific/$WM_OS