reachableroots: silence warning of implicit integer narrowing issued by clang Tested with CFLAGS=-Wshorten-64-to-32 CC=clang which is the default of Mac OS X. Because a valid revnum shouldn't exceed INT_MAX, we don't need long width for large tovisit array.

reachableroots: narrow scope of minidx variable minidx is never used if includepath is false, so let's define it where it is used.