fix "Patch for dos mode nethackrc file on linux"

Reported directly to devteam (12 Dec), user had a config file originally
from MSDOS or Windows and used it on a linux system.  That works as-is
except when it contained an invalid option line.  Feedback was
"ad option line: "whatever-the-line-was
because of the carriage return character staying in the option buffer
after linefeed was stripped off from CR+LF line end.

He included a patch which replaced this existing fixup after fgets()
if ((p = index(buf, '\n')) != 0) *p = '\0';
with a loop over the whole string changing either '\n' or '\r' to '\0'.
This uses
if ((p = index(buf, '\n')) != 0) {
if (p > buf && *(p - 1) == '\r') --p;
*p = '\0';
}
instead.  Ordinarily I would have just cloned the original line and then
substituted \r for \n in the copy, but the report mentioned "I couldn't
get index to work with carriage return".  I don't know what he tried to
do or why simple index(buf,'\r') might not work as intended on his
platform, so I went with something that will work even if index()
behaves as strangely as the report suggested.

(We already have a couple of index(string,'\r') calls in use, but I'm
not going to change those unless someone complains about a problem.)

doc/fixes36.1

@@ -68,6 +68,9 @@ tty: specifying all four of role, race, gender, and alignment still prompted
 unix/X11: in top level Makefile, some commented out definitions of VARDATND
 	misspelled pilemark.xbm (as pilemark.xpm)
 unix/tty: fix compile warning about 'has_colors' for some configurations
+unix: options file with CR+LF line ends and an invalid option line resulted in
+	"ad option line: "whatever-the-line-was
+	because embedded carriage return character changed cursor's position
 win32gui: getversionstring() was overflowing the provided Help About buffer
 win32gui: guard against buffer overflow in in mswin_getlin()
 MacOSX: initial binary release was built from out of date source code that