Fix crash in .paths file handling

When compiling ksh with '-O0 -g -D_std_malloc' on my Mac, the
paths.sh regress test set crashed. This is the test that crashed:

    print 'FPATH=../fun' > bin/.paths
    cat <<- \EOF > fun/myfun
            function myfun
            {
                    print myfun
            }
    EOF
    x=$(FPATH= PATH=$PWD/bin $SHELL -c  ': $(whence less);myfun') 2> /dev/null
    [[ $x == myfun ]] || err_exit 'function myfun not found'

The crash occurred on the second-to-last line. The backtrace
suggests an invalid use of strcpy() with overlapping memory:

0   libsystem_kernel.dylib  __pthread_kill + 10
1   libsystem_pthread.dylib pthread_kill + 284
2   libsystem_c.dylib       abort + 127
3   libsystem_c.dylib       abort_report_np + 177
4   libsystem_c.dylib       __chk_fail + 48
5   libsystem_c.dylib       __chk_fail_overlap + 16
6   libsystem_c.dylib       __chk_overlap + 34
7   libsystem_c.dylib       __strcpy_chk + 64
8   ksh                     path_chkpaths + 1038 (path.c:1534)
9   ksh                     path_addcomp + 1032 (path.c:1481)
10  ksh                     path_addpath + 395 (path.c:1598)
11  ksh                     put_restricted + 626 (init.c:329)
[...]

src/cmd/ksh93/sh/path.c: path_chkpaths():
- When reading the '.paths' file, use memmove(3) instead of
  strcpy(3) as the former does a non-destructive copy with
  tolerance for overlap.

src/cmd/ksh93/sh/path.c

@@ -1531,7 +1531,7 @@ static int path_chkpaths(Shell_t *shp,Pathcomp_t *first, Pathcomp_t* old,Pathcom
 				{
 					char *ptr = stakptr(offset+pp->len+1);
 					if(ep)
-						strcpy(ptr,ep);
+						memmove(ptr,ep,strlen(ep)+1);
 					path_addcomp(shp,first,old,stakptr(offset),PATH_FPATH|PATH_BFPATH);
 				}
 			}