CodingGuidelines: clarify multi-line brace style

There are some "gray areas" around when to omit braces from
a conditional or loop body. Since that seems to have
resulted in some arguments, let's be a little more clear
about our preferred style.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: peff

Documentation/CodingGuidelines

@@ -206,11 +206,38 @@ For C programs:
 		x = 1;
 	}
 
-   is frowned upon.  A gray area is when the statement extends
-   over a few lines, and/or you have a lengthy comment atop of
-   it.  Also, like in the Linux kernel, if there is a long list
-   of "else if" statements, it can make sense to add braces to
-   single line blocks.
+   is frowned upon. But there are a few exceptions:
+
+	- When the statement extends over a few lines (e.g., a while loop
+	  with an embedded conditional, or a comment). E.g.:
+
+		while (foo) {
+			if (x)
+				one();
+			else
+				two();
+		}
+
+		if (foo) {
+			/*
+			 * This one requires some explanation,
+			 * so we're better off with braces to make
+			 * it obvious that the indentation is correct.
+			 */
+			doit();
+		}
+
+	- When there are multiple arms to a conditional and some of them
+	  require braces, enclose even a single line block in braces for
+	  consistency. E.g.:
+
+		if (foo) {
+			doit();
+		} else {
+			one();
+			two();
+			three();
+		}
 
  - We try to avoid assignments in the condition of an "if" statement.