Merge from trunk:

Tolerate argc being zero.

Patch from C. K. Jester-Young.


[SVN r43331]

libs/program_options

@@ -1 +1 @@
-Subproject commit b2a01d940592714798af58babf46dab54b49055c
+Subproject commit f0eae2ccfe657a4d4dde70fb99d22d759fe1a86b