This is to keep the new TrimTree functionality from breaking any code
currently using the public interface. We do this by separating NodeSet
from nodePtrSet and creating different functions for each.

Weblist provides source and assembly combined in a web document.
It needs access to the binary to print the assembly, but currently
refuses to generate the source if the binary can't be find.

Fall back to just generating the source if the binary isn't found.

Reports want to use trimmed paths, not the location in the current
filesystem which may be very verbose.

Currently pprof will look for source files only on the current directory
and its parents. This makes it hard to examine sources on jobs where
there are multiple source trees (eg from different libraries).

Add a variable to provide a search path for source files. It will default
to the cwd, so there will be no change in behavior by default.

Also update the build instructions to use go get