Wconversion: Fix warnings in ex_eval.c.
Wconversion: Fix warnings in file_search.c.
Wconversion: Fix warnings in indent_c.c.
Wconversion: Remove regexp_nfa.c from list.
Wconversion: Change long to int64_t in cursor_shape.c, digraph.c.

Warnings were fixed in #1488.
Merge pull request #1492 from fwalch/fix-wconversion

Fix some more -Wconversion warnings.