Do not use g_io_channel_unix_new() for the win32 platforms.

It is advised to use the more accurate g_io_channel_win32_new_fd() or
g_io_channel_win32_new_socket() because GLib can't differentiate between
file descriptors and sockets on Windows, which outputs a warning when
there is ambiguity.
INSTALL: wrong list numbering.
Bug 733525: check presence of poppler-data (informational only).

As of version 0.4.7, poppler-data has a pkg-config file, allowing us to
verify its presence. The configure summary is only informational, and we
don't impose this version since older versions may still work.
Moreover poppler-data is only a runtime dependency, so you can also add
it afterwards.
Fix generation of AUTHORS

scl tried to modify AUTHORS in 4f852593, but he didn't realize it's
an autogenerated file. This is just repeating his changes on
authors.xml so it matches the modified AUTHORS.