Fix [1864360]: Reenable random generation of crossbow bolts, as it was (erroneously?) removed in r1732, when javelins and sling bullets were introduced. The probability for bolts is slightly greater than that of needles (12 vs. 10), as the probability of randomly generated crossbows is slightly greater than that of blowguns (6 vs. 5). Furthermore, the probability for bolts is lower than the probability for arrows (12 vs. 20), since the former do more damage.

Orc knights and warlords that get crossbows now get orcish ones instead of non-racial ones.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@3315 c06c8d41-db1a-0410-9941-cceddc491573