cmd/pprof: duplicate listings in weblist report

[mdempsky]

When using the interactive "weblist" command, pprof generates multiple reports, one per source file, even though each report contains the same data accumulated across all sources.

E.g.,

go build -gcflags="-cpuprofile=$PWD/cpuprofile.1" -a runtime
cp cpuprofile.1 cpuprofile.2
go tool pprof $(go env GOTOOLDIR)/6g cpuprofile.1 cpuprofile.2

Then try running "list main.main" and "weblist main.main". Notice that weblist shows the same data, but twice because of the two source files.

When you have a lot of source files (e.g., 2000+ from repeatedly building the entire standard library), this makes using weblist impractical, because it constructs the entire report in memory first. (Currently I'm resorting to an ad hoc tool to concatenate CPU profile data.)

[rsc]

Too late for Go 1.5.