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://golang.org/cl/13085043