Remove configure test for boost/function.hpp.

It is no longer used, all code using boost::function was changed to use
std::function from <functional> a while back.
Fix ugly look of plural forms expr field on Windows.
Gracefully handle invalid PO(T) files with duplicate header.

If a file has more than one msgid "" entry without msgctxt (i.e.
header), Poedit would try to parse subsequent occurences as headers.
But they'd typically be empty, resulting in empty header and e.g.  wrong
charset info in Poedit.

Ignore (and discard) any headers other than the first one.  It's too
minor an issue to throw an error about it.
Win: Associate with .po files w/o admin install

If the installer was run without admin prileges, file association
registry keys weren't created, because they are written into admin-only
section of registry.  This allowed user-only installs, but not fully
functional ones.

Fix this by registering the association on first run if there is none.
Fix parsing of language names with scripts

The code for translating human-readable locale names into POSIX-style
codes used icu::Locale::getName(), which creates ICU internal names.
This was incorrect, it could produce names like zh_Hans_CN, as well as
add additional parameters.

Build the code manually from the provided language, country and script
data. Handle the Chinese case specially. Also recognize the Latn script
and translate it into @latin suffix (e.g. sr@latin).

Fixes #100.
Fix handling of files in folders with " in name

On UNIX systems, quote characters are permitted in filenames, but
weren't escaped properly in Poedit.  This conflicted with Poedit's
quoting of all file arguments (which was done to handle _spaces_ in
filenames).

Add a dedicated function for quoting arguments and let it escape " as \"
on UNIX.  This is still not a proper fix, it would be better to avoid
this whole mess by simply passing argv array to wxExecute in the first
place.  That's a bit too risky for 1.6, though, so it will have to be
fixed on master.
Merge branch 'stable'
Add File->Compile to MO...

Add an explicit Compile to MO menu item.  This isn't neeeded all that
much, because Poedit normally compiles the MO automatically, but add it
nevertheless for two reasons:

 * For users who disabled automatic compilation.
 * For discoverability, for users unaware of automatic compilation.
Fix CR/LF inconsistency.
Clear the fuzzy flag when clearing or copying translation

When the translation is cleared or copied from the source, clear its
fuzzy state. Also clear m_isAutomatic for the same reasons.
Add a way to reset the TM.

Add a button to Preferences that purges the translation memory of all
stored translations and lets the user start from scratch.