spellcheck: Fix crash when closing a document quickly after adding data to it

When using timeout callbacks, we need to check the documents are still valid
in the callbacks, in the case they e.g. have been closed since the timeout
started.
Merge pull request #129 from b4n/spellcheck/fix-timeout-callback

spellcheck: Fix crash when closing a document quickly after adding data to it
scope - check if T/B/S file exists (gdb 7.6+ always emits "fullname")
scope - avoid warning when sorting an empty scptreestore branch
scope - remember initial ignore count, version 0.93.2
scope - ChangeLog and NEWS fixes
geanygendoc: Remove some dead code
geanygendoc: Hide a harmless GCC warning

GTokenType don't have named constants for every possible character, so
GCC will warn for byte values not explicitly part of that enumeration,
even though it has a gap designed for any byte to be valid.
cppcheck: allow for extra user and developer flags

Make cppheck calls use flags variables `$(AM_CPPCHECKFLAGS)` (for
developer flags) and `$(CPPCHECKFLAGS)` (for user flags).

This allows both a developer to add specific flags needed to cppcheck
to behave appropriately for the checked code, as well as the users to
specify flags, like e.g. the number ob concurrent jobs.
cppcheck: fix rule portability

`$^` automatic variable is not portable, so explicitly use `$(srcdir)`.

This fixes `make check` with BSD make.
spellcheck: fix checking with cppcheck

cppcheck tests all preprocessor conditionals, but when the code tests
whether one is defined or not it tests simply with it defined or not,
but always to an empty value.  So, code testing whether a macro is
defined, but then relying on the macro expanding to a non-empty value,
cppcheck might very well detect a syntax error.

So, explicitly tell cppcheck to only test the SCE_PAS_DEFAULT=0 case
so it doesn't incorrectly test the SCE_PAS_DEFAULT= case.
geanypy: Fix source file list
scope: Add missing scope.h to the distribution
GeanySendMail: Try to fix a cast-warning
Fix installation path during distcheck

When distchecking we need not to install plugins in the real Geany
libdir, both because it's not writable and because it's a bad idea.

So, pass the appropriate configure flag to override automatic detection
during distcheck's configure run.
Fix some docs in the document module

Signed-off-by: Matthew Brush <matt@geany.org>
gproject: Make toolbar buttons insensitive when no files displayed

This hopefully avoids some confusion regarding what the +/- mean
GeanyLaTeX: Replace NZV-makro with EMPTY-makro
Addons: Replace NZV-makro with EMPTY-makro
GeanyVC: Replace NZV-makro with EMPTY-makro