misc/pprof: pprof http used with net/http/pprof not working on windows/amd64

Removed posix assumptions in temporary file generation
Removed curl dependence
Changed opening of svg file

These must now work including symbol resolution.
[1] go tool pprof <prog_name> http://.../debug/pprof/profile
[2] go tool pprof http://.../debug/pprof/profile

Fixes 6177.

R=golang-dev, alex.brainman, bradfitz, kamil.kisiel
CC=golang-dev
https://codereview.appspot.com/13085043

Committer: Brad Fitzpatrick <bradfitz@golang.org>