functions: fix date calculations

In case date(1) does not support nanosecond resolution, it does
not interpret '%N', and leave it as-is. So we have to remove it.

Note that some versions replaces '%N' with 'N', so we have to
take this into account as well.

Reported-by: Kyle Grieb <grieb.kyle@gmail.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>
(transplanted from bb6e2df2427f3db871721c96ca3226cfa24204bc)

scripts/functions

@@ -235,7 +235,7 @@ CT_Which() {
 # to the highest entire second
 # Usage: CT_DoDate <fmt>
 CT_DoDate() {
-    date "$1" |sed -r -e 's/N$/000000000/;'
+    date "$1" |sed -r -e 's/%?N$/000000000/;'
 }
 
 CT_STEP_COUNT=1