Distinguish between error and timeout in intraline diff error message

When the intraline diff fails, the error message simply says that
there was a server error.  It could be that the reason for failure
is a timeout, but it's not possible to know this from the error
message.

Add a new error message that is displayed when the intraline diff
fails due to timeout.

Also update the documentation to mention that an error message is
displayed if the intraline diff times out.

Change-Id: I93410d853aadc7ed1f6e4324d0578c4bcbe4e195

gerrit-common/src/main/java/com/google/gerrit/common/data/PatchScript.java

@@ -53,6 +53,7 @@ public class PatchScript {
   protected boolean hugeFile;
   protected boolean intralineDifference;
   protected boolean intralineFailure;
+  protected boolean intralineTimeout;
 
   public PatchScript(final Change.Key ck, final ChangeType ct, final String on,
       final String nn, final FileMode om, final FileMode nm,
@@ -60,7 +61,7 @@ public class PatchScript {
       final SparseFileContent ca, final SparseFileContent cb,
       final List<Edit> e, final DisplayMethod ma, final DisplayMethod mb,
       final CommentDetail cd, final List<Patch> hist, final boolean hf,
-      final boolean id, final boolean idf) {
+      final boolean id, final boolean idf, final boolean idt) {
     changeId = ck;
     changeType = ct;
     oldName = on;
@@ -79,6 +80,7 @@ public class PatchScript {
     hugeFile = hf;
     intralineDifference = id;
     intralineFailure = idf;
+    intralineTimeout = idt;
   }
 
   protected PatchScript() {
@@ -152,6 +154,10 @@ public class PatchScript {
     return intralineFailure;
   }
 
+  public boolean hasIntralineTimeout() {
+    return intralineTimeout;
+  }
+
   public boolean isExpandAllComments() {
     return diffPrefs.isExpandAllComments();
   }