userdiff: fix some corner cases in dts regex

While reviewing some dts diffs recently I noticed that the hunk header
logic was failing to find the containing node. This is because the regex
doesn't consider properties that may span multiple lines, i.e.

	property = <something>,
		   <something_else>;

and it got hung up on comments inside nodes that look like the root node
because they start with '/*'. Add tests for these cases and update the
regex to find them. Maybe detecting the root node is too complicated but
forcing it to be a backslash with any amount of whitespace up to an open
bracket seemed OK. I tried to detect that a comment is in-between the
two parts but I wasn't happy so I just dropped it.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Frank Rowand <frowand.list@gmail.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>
Reviewed-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: bebarino

t/t4018/dts-nodes-boolean-prop

@@ -0,0 +1,9 @@
+/ {
+	label_1: node1@ff00 {
+		RIGHT@deadf00,4000 {
+			boolean-prop1;
+
+			ChangeMe;
+		};
+	};
+};

t/t4018/dts-nodes-multiline-prop

@@ -0,0 +1,13 @@
+/ {
+	label_1: node1@ff00 {
+		RIGHT@deadf00,4000 {
+			multilineprop = <3>,
+					<4>,
+					<5>,
+					<6>,
+					<7>;
+
+			ChangeMe = <0xffeedd00>;
+		};
+	};
+};

t/t4018/dts-root

@@ -1,4 +1,4 @@
-/RIGHT { /* Technically just supposed to be a slash */
+/ { RIGHT /* Technically just supposed to be a slash and brace */
 	#size-cells = <1>;
 
 	ChangeMe = <0xffeedd00>;

t/t4018/dts-root-comment

@@ -0,0 +1,8 @@
+/ { RIGHT /* Technically just supposed to be a slash and brace */
+	#size-cells = <1>;
+
+	/* This comment should be ignored */
+
+	some-property = <40+2>;
+	ChangeMe = <0xffeedd00>;
+};

userdiff.c

@@ -25,8 +25,9 @@ IPATTERN("ada",
 	 "|=>|\\.\\.|\\*\\*|:=|/=|>=|<=|<<|>>|<>"),
 PATTERNS("dts",
 	 "!;\n"
+	 "!=\n"
 	 /* lines beginning with a word optionally preceded by '&' or the root */
-	 "^[ \t]*((/|&?[a-zA-Z_]).*)",
+	 "^[ \t]*((/[ \t]*\\{|&?[a-zA-Z_]).*)",
 	 /* -- */
 	 /* Property names and math operators */
 	 "[a-zA-Z0-9,._+?#-]+"