Various fixes for compatibility with latest Julia

[simonster]

• contains(str, str) -> !isempty(search()) (maybe there is a better way?)
• has(set, x) -> contains(set, x)
• keys() now returns a KeyIterator, which breaks _warn_extra_opts because it
  wanted a Vector{Symbol}. Because the type parameter shouldn't be necessary
  and KeyIterator isn't exported from Base, I removed it.

[maleadt]

Gah, I didn't see this PR and fixed most of them myself as well. Anyhow, I needed to fix something else, since search(string, char) doesn't seem to return a range where search(string, string) does:

-            eqrng = search(arg, '=')
-            i = first(eqrng)
-            j = last(eqrng) + 1
+            eq = search(arg, '=')
             if i != 0
-                opt_name = arg[3:i-1]
-                arg_after_eq = arg[j:end]
+                opt_name = arg[3:eq-1]
+                arg_after_eq = arg[eq+1:end]

[carlobaldassi]

Thanks guys, and sorry for the horrible delay! I included these changes in the repo, but I split them into different commits; closing this.