allow full-line comments in tiles source files

Accept
<start of line><optional whitespace>#<anything>
as a comment in win/share/{monsters,objects,other}.txt.  Existing
<start of line><optional whitespace># tile <rest of line>
is grandfathered in as data.

It wouldn't take much more to accept
<data><optional whitespace>#<rest of line>
comments too but this hasn't gone that far.

Reading the colormap at the beginning of each of the three files
used "%[A-Za-z0-i]" to read one characer into a two-character array.
Change that to "%1[A-Za-z0-9]" so that it can't overflow the buffer
if the input data gets accidentally or maliciously mangled.  (Not a
security issue.)

Remove a spurious blank line from objects.txt.

Also, clean up some warnings when compiling gifread.c for gif2txt
although I ultimately didn't do anything with that.

win/share/objects.txt

@@ -3675,7 +3675,6 @@ Z = (195, 195, 195)
   .......KKKAA....
   ........AAA.....
 }
-
 # tile 192 (cubical / amulet of flying)
 {
   ................