Clear %ebp before entering the new thread.

diff --git a/library/port.c b/library/port.c
index af0c244..004f853 100644
--- a/library/port.c
+++ b/library/port.c
@@ -143,6 +143,7 @@
                           "popl %%ebx\n\t"   /* Contains fn in the child */
                           "testl %%eax,%%eax\n\t"
                           "jnz 0f\n\t"
+                          "xorl %ebp,%ebp\n\t"    /* Terminate the stack frames */
                           "call *%%ebx\n\t"       /* Should never return */
                           "xorl %%eax,%%eax\n\t"  /* Just in case it does*/
                           "0:"