go.tools/present: links with the prefix "javascript:" should be executed in the same window.
go.tools/present: links with the prefix "javascript:" should be executed in the same window.

Using url.Parse instead of more ad hoc solution.

R=r
CC=golang-codereviews
https://codereview.appspot.com/47320043

chenjianlong/go.tools,chenjianlong/go.tools,karmakaze/go.tools,karmakaze/go.tools,lattera/go.tools,karmakaze/go.tools,lattera/go.tools,lattera/go.tools,karmakaze/go.tools,karmakaze/go.tools,chenjianlong/go.tools