New DSN parser

+ Set right default addr for net=unix

Go 1.2RC1
BenchmarkParseDSN_new     200000             10545 ns/op            4039
B/op      42 allocs/op
BenchmarkParseDSN_old      10000            233313 ns/op            7588
B/op      91 allocs/op

Go 1.1
BenchmarkParseDSN_new     200000              7940 ns/op            4204
B/op      42 allocs/op
BenchmarkParseDSN_old      10000            264115 ns/op            8083
B/op      91 allocs/op
Escape DSN param values

Not really a behavior change, since it was mostly broken before
DSN param values must be escaped
Fix protocol parsing
Merge pull request #130 from go-sql-driver/dsn_parser

New DSN parser