mksh R52c

R52c is a bugfix-only release:

• Shave 200 bytes off .text by revisiting string pooling
• Fix manpage for ditroff on Schillix
• Use sed 1q instead of unportable head(1)
• Implement underrun debugging tool for area-based memory allocator
• Fix history underrun when first interactive command is entered
• Do not misinterpret “${0/}” as “${0//”, fixes segfault
• Fix display problems with special parameters
• Catch attempt to trim $ and $@ with ?, fixes segfault (Todd Miller did this in 2004 for ${x[]} already, so just sync)
• Fix “command -p” with -Vv to behave as POSIX requires
• Fix recusive parser with active heredocs
• Flush even syntax-failing or interrupted commands to history
• Fix invalid memory access for “'\0'” in arithmetics
• Explicitly reserve SIGEXIT and SIGERR for ksh
• Catch missing here documents at EOF even under “set -n”
• Document Austin#1015 handling (not considered a violation)
• Fix buffer overread for empty nameref targets
• Fix warnings pointed out by latest Debian gcc-snapshot
• Document upcoming set +o changes
• Expand testsuite for command/whence