mksh R57

• Update operating environment reporting for the Macintosh
• make ${foo#'bar'} in here document behave like ksh93
• quote empty strings for re-entry into shell
• Improve documentation, especially for tty states
• Protect against entering line editing with bad saved tty state
• Fix set -o allexport for arrays (which we apparently do)
• Handle lseek(2) returning -1 as pointed out by Coverity Scan
• Fix left-padding UTF-8 strings
• Fix using the “-m” flag on the command line
• Update to UCD 11.0.0
• Fix a segfault using ^W during search in Vi mode
• Fix an error message; add a test for controlling tty
• Permit unsetting LINES and COLUMNS, for those who need it
• Fix manpage bug (RedHat BZ#1612173)
• Minor spelling cleanup
• Unbreak high-bit7 (nōn-ASCII) heredoc separators (LP#1779179)
• Allow dumping high-bit7-char-containing strings in DEBUG mode
• Add some testcases for behaviour questions popped up in IRC
• Trick a GCC warning, to make up for it ignoring lint(1) hints
• Add O_MAYEXEC support for CLIP OS
• Make dup-to-self with ksh-style fd≥3 closing work; catern via IRC
• Add compat glue for newer GNU groff mdoc to the manpages
• Trigger EXIT trap after single-command subshells (Debian #910276)
• Document set -eo pipefail caveat (LP#1804504)
• Fix MKSH_EARLY_LOCALE_TRACKING warning
• Document that, when your Unix is broken, GIGO applies (LP#1817959)
• Improve error message for inaccessible executables (LP#1817789)