Make egrep only set REG_EXTENDED flag.
diff --git a/testsuite/grep/egrep-supports-extended-regexps b/testsuite/grep/egrep-supports-extended-regexps
new file mode 100644
index 0000000..8db154c
--- /dev/null
+++ b/testsuite/grep/egrep-supports-extended-regexps
@@ -0,0 +1 @@
+test x`echo foo | busybox egrep fo+` = xfoo