[moar-gdb.py] change to defaultdict(int)

Shorter, sweeter, and more idiomatic.
[moar-gdb.py] attempt at using unicode box symbols

For the histogram. Should look a bit prettier.
[moar-gdb.py] add shell commands for symlinking
do not stat a file without filename

When we are reading from STDIN, we have no filename set, so dont try to stat a real file.
This patch was brought to you by jnthn++ :o)
pass STDIN to subprocess in shell()

... so the child process can read from our STDIN when it creates a prompt.
Fix resolve_host_name for IPv6
Add native calling ops to oplist.
Add nativecall ops to interp.c; stub functions.
small cleanups
Revert "[moar-gdb.py] attempt at using unicode box symbols"

This reverts commit 941000b2f9c306448fb06906e502bda121e13eb8.

gdb insists that our terminal can only do ascii.
[moar-gdb.py] MVMString isn't null-terminated
[moar-gdb.py] don't explode due to encoding
[moar-gdb.py] hooray for no coercive operators!
[moar-gdb.py] count strings in the string histogram
[moar-gdb.py] string histograms end up being really long.
[moar-gdb.py] analyze objects in the overflow
Add NativeCall REPR.
Add dyncall include.
Implement nativecallbuild op.
Add encode all the string UTF-16 function.