Check errno, not the result of symlink(), for EEXIST.

Resolves #1305.
add user_{fp,}regs_struct to kernel_abi.h
use rr-defined user_regs_struct as basis for Registers

This change ensures that user_regs_struct is defined exactly like the
kernel expects; otherwise, numerous test failures would ensue.  As a
bonus fix, the format strings for dumping register contents must also be
changed to reflect the portable definition of user_regs_struct.
Track whether advance_to has seen a full register state match with some non-zero rbcs left, and report it when we fail to hit our target.

Also, allow rbc slack when we get a register state match a little late. We
might as well allow the match instead of dying.
Allow files with different minor device numbers to be treated as identical if the major device number is 0.

/proc/<pid>/maps and 'stat' have been observed to disagree on the minor
device number for a mapped file. This may be due to btrfs. In the observed
cases, the major device number is zero. Inode numbers still agree.
Improve VMWare warning.
Bump version to 2.0.0.
Reformat C/C++ sources using clang-format.

From now on, reformat your source code using
  find src include -name '*.cc' -or -name '*.h' -or -name '*.c'|xargs clang-format -i -style=file
before checking in.

Note that tabs are now prohibited in C/C++ files.
Update contribution instructions regarding `clang-format`.
Fix markup.
Fix up some leftover formatting issues.

All tabs have been removed from all source files.
Don't need to call stop_hpc from emulate_async_signal.
Rework perfcounter interface into a C++ class.

Starts the process of renaming rbc/rcb to 'ticks'.

Stops disabling counters before we close the fd. That's unnecessary
overhead.

Instead of using an #ifdef to guard the extra perf counters,
use a static bool function instead. #ifdefs are evil.
Rename hpc.h/.cc to PerfCounters.h/.cc.
only check for $esi mutation on x86 in validate_args
Split compressed_io.h/.cc into CompressedReader.h/.cc and CompressedWriter.h/.cc.
Fix #include guard symbol.
Remove 'byte' typedef and just use uint8_t instead.
Rename supported_arch to SupportedArch.
Move SupportedArch to kernel_abi.h