1.0.12.22: Optimize READ-SEQUENCE into strings and READ-LINE

1.0.12.22: Optimize READ-SEQUENCE into strings and READ-LINE

       * Have READ-LINE and READ-SEQUENCE directly use the cin buffer whenever
         one exists, instead of going through FAST-READ-CHAR. READ-LINE already
         did this in some circumstances, but often .
       * READ-LINE on normal data with short lines is around 50% faster, with
         abnormally long lines about 75% faster. (On my laptop -- IIRC the
         difference was smaller on a workstation).
       * READ-SEQUENCE into a simple string is up to 80% faster.
       * Modify FAST-READ-CHAR-REFILL a bit to make it nicer to use in the
         non-read-char cases.
       * Fix a utf-8 resyncing bug in READ-LINE (masked by the test case
         in external-format.impure not having a newline at the end, which
         caused READ-LINE to always take the slow path).