Pass terminal dimensions to git by setting COLUMNS and LINES

This partially reverts "Show diff stats as wide as the terminal" (commit
a7eb305) which passed the terminal
width to git-diff using `--stat=%(width)`. This feature was introduced
in Git version 1.7.10 released 2013-04-06 and causes problems for older
versions of Git.

It turns out that Git will automatically read $COLUMNS when showing diff
stats, so the same effect can be achieved by passing the terminal
dimensions using environment variables.

Fixes GH-151, "Broken commit rendering on Ubuntu 10.04" since
incompatibilitis with older versions of Git is no longer an issue.
Tested using `tig 1f384f3`.

manual.txt

@@ -162,7 +162,6 @@ following variables.
 |%(fileargs)		|The file arguments passed on the command line.
 |%(diffargs)		|The diff options passed on the command line.
 |%(prompt)		|Prompt for the argument value.
-|%(width)		|The view width.
 |=============================================================================
 
 Example user-defined commands:

tig.c

@@ -22,6 +22,9 @@ static void warn(const char *msg, ...) PRINTF_LIKE(1, 2);
 static void report(const char *msg, ...) PRINTF_LIKE(1, 2);
 #define report_clear() report("%s", "")
 
+static bool set_environment_variable(const char *name, const char *value);
+static bool set_int_environment_variable(const char *name, int value);
+
 
 enum input_status {
 	INPUT_OK,
@@ -2496,6 +2499,8 @@ resize_display(void)
 	/* Setup window dimensions */
 
 	getmaxyx(stdscr, base->height, base->width);
+	set_int_environment_variable("COLUMNS", base->width);
+	set_int_environment_variable("LINES", base->height);
 
 	/* Make room for the status window. */
 	base->height -= 1;
@@ -3077,9 +3082,6 @@ format_expand_arg(struct format_context *format, const char *name)
 		return string_format_from(format->buf, &format->bufpos, "%s", value);
 	}
 
-	if (!prefixcmp(name, "%(width)"))
-		return string_format_from(format->buf, &format->bufpos, "%d", format->view->width);
-
 	for (i = 0; i < ARRAY_SIZE(vars); i++) {
 		const char *value;
 
@@ -4443,7 +4445,7 @@ diff_open(struct view *view, enum open_flags flags)
 {
 	static const char *diff_argv[] = {
 		"git", "show", opt_encoding_arg, "--pretty=fuller", "--no-color", "--root",
-			"--patch", "--stat=%(width)",
+			"--patch-with-stat",
 			opt_notes_arg, opt_diff_context_arg, opt_ignore_space_arg,
 			"%(diffargs)", "%(commit)", "--", "%(fileargs)", NULL
 	};
@@ -8184,6 +8186,15 @@ set_environment_variable(const char *name, const char *value)
 	return FALSE;
 }
 
+static bool
+set_int_environment_variable(const char *name, int value)
+{
+	char buf[SIZEOF_STR];
+
+	return string_format(buf, "%d", value)
+	    && set_environment_variable(name, buf);
+}
+
 static void
 set_work_tree(const char *value)
 {

tigrc.5.txt

@@ -392,7 +392,6 @@ is run. Valid variable names are:
 |%(fileargs)		|The file arguments passed on the command line.
 |%(diffargs)		|The diff options passed on the command line.
 |%(prompt)		|Prompt for the argument value.
-|%(width)		|The view width.
 |=============================================================================
 
 As an example, the following external command will save the current commit as