[patchbomb] prepend leading zeros in the "[PATCH N of M]" string Without this patch, if one tries to send a patch bomb with more than 9 patches, the resulting subjects are not easily alphabetically sortable. For example: ... [PATCH 9 of 10] [PATCH 10 of 10] This patch prepends as many leading zeros as necessary. E.g., [PATCH 09 of 10] or [PATCH 009 of 100]