remove_words! fails for long terms & terms with punctuation

Because remove_words! uses regex matching even for string input, it fails on actually-present terms if those terms are larger than the maximum pattern size accepted by PCRE. Actually-present terms also fail if they contain regex-like punctuation. This produces an error message that doesn't specify the failed pattern, and furthermore aborts remove_words! entirely.

The same problem occurs in remove_sparse_terms! and remove_frequent_terms!, since these also file down to a call to remove_pattern.

Would it be possible to force only string-literal substitution in the case where an array of type String is passed (and only use regex if the items passed are actually typed as regular expressions)?