450f14521b
1. Ignore whitespace because migemo doesn't generate any useful regexp for whitespace. 2. Fix not to escape any ASCII characters (e.g. `*`, `.`) if migemo is enabled, because `s:convertMigemo()` will replace them with migemo-regexps. 3. Remove verifying `re` in `s:convertMigemo()`, because `s:should_use_migemo()` already verified it.