relpath: Properly handle a "." directory name.

tools/relpath.c

diff --git a/tools/relpath.c b/tools/relpath.c
index ceb1d36..117ecef 100644
--- a/tools/relpath.c
+++ b/tools/relpath.c
@@ -30,6 +30,9 @@
 #define DIR_END(p)  (*(p) == 0 || *(p) == '/')
     const char *start;
 
+    /* a path of "." is equivalent to an empty path */
+    if (!strcmp( from, "." )) from = "";
+
     *dotdots = 0;
     for (;;)
     {