Disable SHOPT_EDPREDICT compile-time option by default

It's experimental, undocumented, at least somewhat broken, and gets
in the way if you type a comment. Should not be enabled by default,
at least not until someone steps up to fix it properly.

This commit also updates the descriptions of the option to clarify
that this provides a pattern-based history search menu. "Predictive
editing" is a misnomer as this does not predict anything.

Note that Solaris already disables it by default:
https://github.com/oracle/solaris-userland/blob/master/components/ksh93/patches/165-CR7186440_ksh93_disable_predictive_editing.patch

Discussion: #233

src/cmd/ksh93/README

@@ -47,12 +47,13 @@ The options have the following defaults and meanings:
                      process substitutions. On by default on OSs with /dev/fd.
     DYNAMIC      on  Dynamic loading of builtins. (Requires dlopen() interface.)
     ECHOPRINT    off Make echo equivalent to print.
-    EDPREDICT    on  Enables predictive editing. As you type a line beginning
+    EDPREDICT    off Enables history pattern search menu. As you begin a line
                      with a #, the following characters are treated as a shell
                      pattern and cause matching lines from the history file to
                      be displayed as a numbered list as you type. You can
                      scroll up and down this list or you can use <ESC>nTAB to
                      make this the current line (n defaults to 1 if omitted).
+                     Experimental. Bugs: https://github.com/ksh93/ksh/issues/233
     ESH          on  Compile with emacs command line editing.  The original
                      emacs line editor code was provided by Mike Veach at IH.
     FILESCAN     on  Experimental option that allows fast reading of files

src/cmd/ksh93/SHOPT.sh

@@ -2,6 +2,8 @@
 # Compile-time SHOPT_* options for ksh93.
 # 1 to enable, 0 to disable, empty value to probe.
 #
+# For a more complete description of the options, see src/cmd/ksh93/README.
+#
 
 SHOPT 2DMATCH=1				# two dimensional ${.sh.match} for ${var//pat/str}
 SHOPT ACCT=				# accounting
@@ -16,7 +18,7 @@ SHOPT CRNL=				# accept MS Windows newlines (<cr><nl>) for <nl>
 SHOPT DEVFD=				# use /dev/fd instead of FIFOs for process substitutions
 SHOPT DYNAMIC=1				# dynamic loading for builtins
 SHOPT ECHOPRINT=			# make echo equivalent to print
-SHOPT EDPREDICT=1			# predictive editing
+SHOPT EDPREDICT=0			# History pattern search menu (type #<pattern>, then ESC <number> TAB). Experimental.
 SHOPT ESH=1				# emacs/gmacs edit mode
 SHOPT FILESCAN=1			# fast file scan
 SHOPT FIXEDARRAY=1			# fixed dimension indexed array