* Make binutils thread safe.

binutils is now used from multiple goroutines when the
web interface is enabled (since http server spins up a new
goroutine for each request). Added appropriate synchronization
to various objects in binutils to provide the appropriate
thread-safety.

In addition, added a bunch of tests:

. Test parsing of nm output.
. Tests for Binutils methods.
. Test llvm-symbolizer interface (using an llvm-symbolizer emulator).

* Fix go vet errors about unkeyed literals.

* copy stderr to figure out test failures

* Make shell script portable.

* Update comments to match new var name.

* Give a name to the embedded Mutex field in addr2Liner.

- Remove dead code, unnecessary conversions
- Consistently use a single space after period

This will enable symbolization support for Go on Mac OS
It re-enables symbolization using debug/pprof/symbol on
Go profiles in the legacy format, and implements basic
mach-O support on the binutils package.

The names produced by addr2line are often incomplete.  Fix this by
falling back to nm to get function names and using the nm-provided
name if it is longer.

Provide native Go mocks for binutils to use during testing, instead of
relying on shell-script mocks of those tools.

Also update the build instructions to use go get