fix potential buffer overflow in SYSTEM::hostname

gethostname() may cause an error or it might need more space than any given static buffer provides. In both cases the data in the buffer might not be null terminated!

Also String() uses fromAscii(). While I guess this should be ok for host names I think it is always better to use fromLocal8Bit(). I think the user name might not be 7-bit ASCII.
make name buffer even larger

I just realized there are some quite large host names out there. E.g. www.llanfairpwllgwyngyllgogerychwyrndrobwyll-llantysiliogogogoch.com
Merge pull request #34 from panzi/patch-1

fix potential buffer overflow in SYSTEM::hostname