Added support for @-arguments (that read files containing more
arguments) like javac does (and removed it from the low-level compiler
so we don't try to substitute twice). This is one thing needed for #1076
If the current tool is a CeylonBaseTool and it has its `cwd` field set we pre-load the correct CeylonConfig before running the tool and restore the current one (if any) when it returns. That way one tool can call another with a different `cwd` and still work properly. (Somewhat related to ceylon/ceylon-common#9)
The CompilerConfig now properly handles the `cwd` option if it was set in the options (see ceylon/ceylon-common#9)
THe Ceylon file manager now uses a CeylonConfig kept in the compiler's Context instead of the thread local one (see ceylon/ceylon-common#9)
Made Ceylon file manager lookup of the default out repository use the proper CeylonConfig obtained from the Context (see ceylon/ceylon-common#9)