Fix build with wxUSE_FFILE=0.

Add the missing "#if wxUSE_FFILE" checks and add fallbacks to wxFile if it's
available.

Closes #15353.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74596 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Allow using custom method names in wxHTTP.

Add wxHTTP::SetMethod().

Also simplify the code by determining the method to use in Connect() instead
of doing it in BuildRequest() itself.

Get rid of the now unused wxHTTP_Req enum.

Closes #15354.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74597 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Add a configuration file for Travis CI system.

Try to use Travis in addition to buildbot to see if it can be useful for us.

Closes #15355.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74598 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775