Fix more bugs that occur when enabling ASan (#293)

src/cmd/ksh93/{bltins/typeset,sh/name,sh/nvtree,sh/nvtype}.c:
- Replace more instances of memcmp with strncmp to fix
  heap-buffer-overflow errors when running the regression tests
  with ASan enabled.

src/cmd/ksh93/edit/vi.c:
- Fix an invalid dereference of the 'p' pointer to fix a crash in
  vi mode when entering a comment in the command history. This
  bugfix was backported from ksh2020:
  https://github.com/att/ast/issues/798

src/cmd/ksh93/tests/pty.sh:
- Add a regression test for the vi mode crash.

src/cmd/ksh93/tests/pty.sh

@@ -826,5 +826,20 @@ w :\E_
 r ^:test-2: : One\\ "Two Three"\$'Four Five'\.mp3\r\n$
 !
 
+# err_exit #
+((SHOPT_VSH)) && tst $LINENO <<"!"
+L crash when entering comment into history file (vi mode)
+# https://github.com/att/ast/issues/798
+
+d 15
+p :test-1:
+c foo \E#
+r ^:test-1: #foo\r\n$
+w hist -lnN 1
+r ^:test-2: hist -lnN 1\r\n$
+r \t#foo\r\n$
+r \thist -lnN 1\r\n$
+!
+
 # ======
 exit $((Errors<125?Errors:125))