patch: tweaks

1) Eliminate spurious warnings about possibly reduced hunks.  Instead only
note a possible location if we don't find a non-reversed place to apply it.
(Otherwise, hunks that move code forward around within a file look reversed at
the removal site.)

2) Open the source file read-only, so we can apply patches to read-only files.

Signed-off-by: Rob Landley <rob@landley.net>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/editors/patch.c b/editors/patch.c
index c40f541..0bde2ca 100644
--- a/editors/patch.c
+++ b/editors/patch.c
@@ -344,14 +344,12 @@
 		while (plist && *plist->data == "+-"[reverse]) {
 			if (data && !strcmp(data, plist->data+1)) {
 				if (!backwarn) {
-					backwarn++;
+					backwarn = TT.linenum;
 					if (option_mask32 & FLAG_IGNORE) {
 						dummy_revert = 1;
 						reverse ^= 1;
 						continue;
 					}
-					fdprintf(2,"Possibly reversed hunk %d at %ld\n",
-						TT.hunknum, TT.linenum);
 				}
 			}
 			plist = plist->next;
@@ -364,6 +362,10 @@
 			// Does this hunk need to match EOF?
 			if (!plist && matcheof) break;
 
+			if (backwarn)
+				fdprintf(2,"Possibly reversed hunk %d at %ld\n",
+					TT.hunknum, TT.linenum);
+
 			// File ended before we found a place for this hunk.
 			fail_hunk();
 			goto done;
@@ -592,7 +594,7 @@
 						TT.filein = xopen3(name, O_CREAT|O_EXCL|O_RDWR, 0666);
 					} else {
 						printf("patching file %s\n", name);
-						TT.filein = xopen(name, O_RDWR);
+						TT.filein = xopen(name, O_RDONLY);
 					}
 					TT.fileout = copy_tempfile(TT.filein, name, &TT.tempname);
 					TT.linenum = 0;