Reduce parse-options.o dependencies

Currently parse-options.o pulls quite a big bunch of dependencies.
his complicates it's usage in contrib/ because it pulls external
dependencies and it also increases executables size.

Split off less generic and more internal to git part of
parse-options.c to parse-options-cb.c.

Move prefix_filename function from setup.c to abspath.c. abspath.o
and wrapper.o pull each other, so it's unlikely to increase the
dependencies. It was a dependency of parse-options.o that pulled
many others.

Now parse-options.o pulls just abspath.o, ctype.o, strbuf.o, usage.o,
wrapper.o, libc directly and strlcpy.o indirectly.

Signed-off-by: Dmitry Ivankov <divanorama@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

abspath.c

@@ -139,3 +139,31 @@ const char *absolute_path(const char *path)
 	}
 	return buf;
 }
+
+/*
+ * Unlike prefix_path, this should be used if the named file does
+ * not have to interact with index entry; i.e. name of a random file
+ * on the filesystem.
+ */
+const char *prefix_filename(const char *pfx, int pfx_len, const char *arg)
+{
+	static char path[PATH_MAX];
+#ifndef WIN32
+	if (!pfx_len || is_absolute_path(arg))
+		return arg;
+	memcpy(path, pfx, pfx_len);
+	strcpy(path + pfx_len, arg);
+#else
+	char *p;
+	/* don't add prefix to absolute paths, but still replace '\' by '/' */
+	if (is_absolute_path(arg))
+		pfx_len = 0;
+	else if (pfx_len)
+		memcpy(path, pfx, pfx_len);
+	strcpy(path + pfx_len, arg);
+	for (p = path + pfx_len; *p; p++)
+		if (*p == '\\')
+			*p = '/';
+#endif
+	return path;
+}