Proper ISE version is detetcted basing on XILINX variable.
Afterwards, a path to ISE installtion (default) is put
into the makefile.

From now on, it shouldn't complain about a missing module,
if in fact it is already fetched

Action variable from the top manifest is now passed
everywhere. It means, it is present when parsing all
manifests and it can be used for any purposes.

If a module has "fetchto" variable defined, then all
it's modules are fetched to this destination. If the
variable is indefined, then it is taken the parent.

Now modules to be fetched are recognized properly