Partially undo change that prevented SED, GREP, EGREP and AR from being changed by libtool or autoconf.

definition which might be defined in config.h or config-*.h files

but it breaks aclocal execution on some systems, with the following error:

Can't locate object method "rel2abs" via package "File::Spec" at /usr/local/bin/aclocal line 256.

address in an IPv6 capable libcurl.

needed, and being able to define it if appropriate for further configure tests
as well as for the generated config file.

  overrun" (http://curl.haxx.se/bug/view.cgi?id=2026240) identifying two
  problems, and providing the fix for them:

  - CURL_READFUNC_PAUSE did in fact not pause the _sending_ of data that it is
    designed for but paused _receiving_ of data!

  - libcurl didn't internally set the read counter to zero when this return
    code was detected, which would potentially lead to junk getting sent to
    the server.

that other package's underquoted m4 function definitions have on ours.

http://sources.redhat.com/automake/automake.html#Extending-aclocal documents
that starting with Automake 1.8, aclocal will warn about all underquoted calls
to AC_DEFUN due to the fact that in a single aclocal run it might include more
than once all .m4 files which it finds available, this includes .m4 files from
other software packages.

If the first argument to AC_DEFUN is underquoted and the same macro is included
more than once, successive inclusions after the first one will expand the macro
instead of assuming it is the same as the first one included.

needed, and being able to define it if appropriate for further configure tests
as well as for the generated config file.

Introduced reentrant.m4 intended for our reentrant related autotools/m4 macros.

lines ending in \r.

defined by the libcurl API. Also changed curl_easy_setopt examples to
pass longs where appropriate.

  non-zero with the fixed value of 1. We should strive at making options
  support '1' for enabling them mentioned explicitly, as that then will allow
  us for to extend them in the future without breaking older programs.

actually verify if the test is properly working

setting as the one actually used when finally building the library.

checks for gethostbyname_r with 5 and 6 args now also done with -D_REENTRANT

data type for systems where this sixth argument is prototyped as a void pointer.

Start of thread: http://curl.haxx.se/mail/lib-2008-07/0153.html