travis-ci bits: try to avoid failure-flagging on transient connectivity issues

Attempt to test whether Lua fetch succeeded (and pdcurses for windows
and msdos as well)

If those prerequisite fetches and untars didn't work, just exit without
marking the travis-ci build as a failure so that the development team
isn't notified about something transient that they don't need to fix
in the code.

sys/msdos/msdos-cross-compile.sh

@@ -74,6 +74,12 @@ fi
 
 cd ../
 
+# Don't fail the build if lua fetch failed because we cannot do anything about it
+# but don't bother proceeding forward either
+if [ ! -d "lib/lua-$LUA_VERSION/src" ]; then
+        exit 0
+fi
+
 #echo after dos extender
 
 cd src

sys/winnt/travis-gcc.sh

@@ -2,7 +2,7 @@ set -x
 mkdir -p lib
 cd lib
 git clone --depth 1 https://github.com/wmcbrine/PDCurses.git pdcurses
-git clone --depth 1 https://github.com/universal-ctags/ctags.git ctags
+#git clone --depth 1 https://github.com/universal-ctags/ctags.git ctags
 curl -R -O http://www.lua.org/ftp/lua-5.3.5.tar.gz
 tar zxf lua-5.3.5.tar.gz
 cd ../