Auto merge of #24560 - kwantam:apply_table_opt, r=alexcrichton

Auto merge of #24560 - kwantam:apply_table_opt, r=alexcrichton

Apply optimization described in
https://github.com/rust-lang/regex/pull/73#issuecomment-93777126
to rust's copy of `unicode.py`.

This shrinks librustc_unicode's tables.rs from 479kB to 456kB,
and should improve performance slightly for related operations
(e.g., is_alphabetic(), is_xid_start(), etc).

In addition, pull in fix from @dscorbett's commit
d25c39f86568a147f9b7080c25711fb1f98f056a in regex, which
makes `load_properties()` more tolerant of whitespace
in the Unicode tables. (This fix does not result in any
changes to tables.rs, but could if the Unicode tables
change in the future.)