PathParam declared as a fragment within a path segment is not recognized

[elakito]

When a path parameter is declared as a fragment in a path segment, as in

paths:
  /foo/bar{fragment}:

go-openapi's validator fails to recognize this parameter and results in the error:
2017/11/10 15:54:50 path param "fragment" is not present in path "/foo/bar{fragment}"

I noticed this problem when I was using go-swagger and the error was coming from the validation code of go-openapi

I will add a PR that fixes the validator (in spec.go)'s path handling and with this change. Please take a look at it.

Thank you

Regards, aki