Fix 'command -p' lookup if hash table entry exists (re: c9ccee86)

If a command's path was previously added to the hash table as a
'tracked alias', then the hash table entry was used, bypassing
the default utility path search activated by 'command -p'.

'command -p' activates a SH_DEFPATH shell state. The bug was caused
by a failure to check for this state before using the hash table.
This check needs to be added in four places.

src/cmd/ksh93/sh/path.c,
src/cmd/ksh93/sh/xec.c:
- path_search(), path_spawn(), sh_exec(), sh_ntfork(): Only consult
  the hash table, which is shp->track_tree, if the SH_DEFPATH shell
  state is not active.

src/cmd/ksh93/tests/path.sh:
- Add regress tests checking that 'command -p' and 'command -p -v'
  still search in the default path if a hash table entry exists for
  the command searched.

NEWS

@@ -3,6 +3,12 @@ For full details, see the git log at: https://github.com/ksh93/ksh
 
 Any uppercase BUG_* names are modernish shell bug IDs.
 
+2020-08-17:
+
+- 'command -p' incorrectly used the hash table entry (a.k.a. tracked alias)
+  for a command if its path was previously hashed. It has now been fixed so
+  it never consults the hash table.
+
 2020-08-16:
 
 - Fixed 'command -x' on macOS, Linux and Solaris by accounting for a 16-byte