* lib/autoconf/status.m4 (_AC_OUTPUT_FILES_PREPARE): When

* lib/autoconf/status.m4 (_AC_OUTPUT_FILES_PREPARE): When
creating the awk substitution script, handle one input line at a
time, so that the maximum length of a substituted (multi-line)
value is not limited by the size of the sed pattern space.
The trade-off is a slightly repetitive sed script.
* doc/autoconf.texi (Limitations of Usual Tools): Branch labels
can only have up to 7 characters, due to Solaris 10 /bin/sed.
* tests/torture.at (Substitute a 2000-byte string): Increase the
test with several long lines, they should not be caught by sed
limits any more.