index: reuc and name entrycounts should be size_t

For the REUC and NAME entries, we use size_t internally, and we take
size_t for the get_byindex() functions, but the entrycount() functions
strangely cast to an unsigned int instead.
Merge pull request #2775 from ethomson/index_entrycounts

index: reuc and name entrycounts should be size_t