Only warn when trying to modify read-only files

Failing when trying to patch read-only files causes various users of patch to
break.  Instead, warn by default and introduce a command line option for
choosing a different behavior.
* patch.man: Describe the new behavior and command-line option.
* src/patch.c (read_only_behavior): New variable.
(main): Implement the new behavior.
(longopts): Add the new --read-only option.
(option_help): Describe the new behavior.
(get_some_switches): Recognize the new --read-only option.

1 files changed, 6 insertions, 2 deletions

diff --git a/patch.man b/patch.man
index 02e6b90..b0ee8c1 100644
--- a/patch.man
+++ b/patch.man
@@ -314,6 +314,10 @@ and patches should be generated by
 .B "diff\ \*=binary"
 when line endings are significant.)
 .TP
+\fB\*=read\-only=\fP\fIbehavior\fP
+Behave as requested when trying to modify a read-only file: \fBignore\fP the
+potential problem, \fBwarn\fP about it (the default), or \fBfail\fP.
+.TP
 \fB\-c\fP  or  \fB\*=context\fP
 Interpret the patch file as a ordinary context diff.
 .TP
@@ -356,8 +360,8 @@ removes a file, it also attempts to remove any empty ancestor directories.
 \fB\-f\fP  or  \fB\*=force\fP
 Assume that the user knows exactly what he or she is doing, and do not
 ask any questions.  Skip patches whose headers
-do not say which file is to be patched; patch files even though they are
-read-only or have the wrong version for the
+do not say which file is to be patched; patch files even though they have the
+wrong version for the
 .B Prereq:\&
 line in the patch; and assume that
 patches are not reversed even if they look like they are.