Fix for <http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=638258>:
Distcc fails to build on hurd-i386 because it relies on PATH_MAX being
defined.

build problem with -Werror due to ignoring return value of 'chdir'.

Fixes issue 43 <http://code.google.com/p/distcc/issues/detail?id=43>.
As mentioned in issue 34 <http://code.google.com/p/distcc/issues/detail?id=34>,
hosts with both IPv4 and IPv6 addresses showed up twice if avahi is
IPv6-enabled.  So, filter out duplicates using the service name.

* Still needs configure flag masking for IPv6 literals
* Needs some fix for zeroconf hosts that have both and IPv6 and IPv4 address

and gcc-id.c.  Remove Google copyright notice from src/gcc-id.c, since
the Google changes to that file were very minor.

(typically the only change is in the FSF street address).  Add Google
copyright line in some places it was missing.  Add GPLv2 notice to
avahi patches.

OKed by fergus

Also, fix the emacs var-setting line: it was missing a semicolon
before, which means the entire line was being ignored.

No contentful change.

Reviewed by fergus@google.com

lines.  Fixed up resulting mis-indented code I noticed (mostly in
files that used 8 space indents, or used 4-space and 8-space indents
in the same file (!)).  Added the emacs tab-var setting for all files,
not just some of them.

I also added in copyright notices for files I noticed that didn't have
them.  We'll want to do another pass-through to fix these up properly,
though.

I used the following perl snippet to check for mis-indented code after
converting tabs to whitespace:

  $ for i in *.{c,h}; do echo $i; perl -nle 'if ($indent > 0) {$sp=" " x $indent; /^$sp[^ ]/ && print "$.: $_"; $indent=0;}; if (/^( *).*{/ ) {$indent=length($1);} else {$indent=0;}' $i; done | less

It had false positives, but hopefully didn't miss anything.

Reviewed by klarlund@google.com

(1) Correct order of -Is in Makefile.

(2) remove unnessary PATH modification in configure.ac (this is fergus's
suggestion -- hopefully this will do, this replaces a circumvention mechanism I
had originally concocted.

(3) Fix place of the include of popt in CPPFLAGS.

(4) Convert quoted includes of config.h to angle bracket includes so that the
build version, not the source version, of this file is picked up.

The order of -Is in the build system is wrong: it contradicts the
VPATH mechanism.  

This means that builds in a build directory different from that
of the source (distribution) directory will find wrong files even
after the hapless developer has issued only a 'configure' command
in the source directory (but not actually 'made' any thing
there).  For in that case, the src/config.h will be generated in
the source directory and this will be the file picked in the
build directory even if that directory has it's own src/config.h.
This can lead to wrong builds and it can be hard to diagnose the
problem.

Currently, this what CPPFLAGS end up being (as found in the
generated Makefile):

  CPPFLAGS =  -DHAVE_CONFIG_H -D_GNU_SOURCE \
              -I../distcc/popt -I../distcc/src \
              ${DIR_DEFS} \
              -Isrc -Ilzo \
              -I"$(srcdir)/src" -I"$(srcdir)/lzo" \

Here my source dir was ../distcc.  

The presence of '-I../distcc/popt' in front of -Isrc is the exact
opposite of the semantics of VPATH mechanism, which looks for
files in the build directory, then in the source directory.  

Also, note the remarks in:

  http://www.gnu.org/software/autoconf/manual/autoconf.html#Configuration-Headers

(they do not quite correctly discuss the search path, btw).

TESTING: I verified that with a corrupted config.h file in the source directory,
building now succeeds.

Also: make distcheck (it fails the same place as before: this is corrected in
another change of mine --- I'll verify that with that change in place, this
change makes 'make distcheck' succeed.)

REVIEWERS: fergus@google.com, csilvers@google.com