The prototype of set_file_slot already includes API_EXPORT_NONSTD... fix

the declaration.

BTW, I think _NONSTD is only required for functions which have variable
length parameter lists.  i.e. bputs and rputs... but *not* vbprintf since
that has a fixed parameter list.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@80269 13f79535-47bb-0310-9956-ffa450edef68