Rename safe_strncpy() to strlcpy().

This cleans up the use of safe_strncpy() even more.  Since it has the
same semantics as strlcpy() use this name instead.  Also move the
definition from inside path.c to its own file compat/strlcpy.c, and use
it conditionally at compile time, since some platforms already has
strlcpy().  It's included in the same way as compat/setenv.c.

Signed-off-by: Peter Eriksen <s022018@student.dtu.dk>
Signed-off-by: Junio C Hamano <junkio@cox.net>

compat/strlcpy.c

@@ -0,0 +1,13 @@
+#include <string.h>
+
+size_t gitstrlcpy(char *dest, const char *src, size_t size)
+{
+	size_t ret = strlen(src);
+
+	if (size) {
+		size_t len = (ret >= size) ? size - 1 : ret;
+		memcpy(dest, src, len);
+		dest[len] = '\0';
+	}
+	return ret;
+}