Windows: Make the pager work.

Since we have neither fork() nor exec(), we have to spawn the pager and
feed it with the program's output.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>

pager.c

@@ -1,12 +1,13 @@
 #include "cache.h"
 
 /*
- * This is split up from the rest of git so that we might do
- * something different on Windows, for example.
+ * This is split up from the rest of git so that we can do
+ * something different on Windows.
  */
 
 static int spawned_pager;
 
+#ifndef __MINGW32__
 static void run_pager(const char *pager)
 {
 	/*
@@ -22,11 +23,31 @@ static void run_pager(const char *pager)
 	execlp(pager, pager, NULL);
 	execl("/bin/sh", "sh", "-c", pager, NULL);
 }
+#else
+#include "run-command.h"
+
+static const char *pager_argv[] = { "sh", "-c", NULL, NULL };
+static struct child_process pager_process = {
+	.argv = pager_argv,
+	.in = -1
+};
+static void wait_for_pager(void)
+{
+	fflush(stdout);
+	fflush(stderr);
+	/* signal EOF to pager */
+	close(1);
+	close(2);
+	finish_command(&pager_process);
+}
+#endif
 
 void setup_pager(void)
 {
+#ifndef __MINGW32__
 	pid_t pid;
 	int fd[2];
+#endif
 	const char *pager = getenv("GIT_PAGER");
 
 	if (!isatty(1))
@@ -45,6 +66,7 @@ void setup_pager(void)
 
 	spawned_pager = 1; /* means we are emitting to terminal */
 
+#ifndef __MINGW32__
 	if (pipe(fd) < 0)
 		return;
 	pid = fork();
@@ -72,6 +94,20 @@ void setup_pager(void)
 	run_pager(pager);
 	die("unable to execute pager '%s'", pager);
 	exit(255);
+#else
+	/* spawn the pager */
+	pager_argv[2] = pager;
+	if (start_command(&pager_process))
+		return;
+
+	/* original process continues, but writes to the pipe */
+	dup2(pager_process.in, 1);
+	dup2(pager_process.in, 2);
+	close(pager_process.in);
+
+	/* this makes sure that the parent terminates after the pager */
+	atexit(wait_for_pager);
+#endif
 }
 
 int pager_in_use(void)