NautilusIdeviceinfoPage: Chain up to parent class dispose
Fix 'self-assignment' in nautilus_ideviceinfo_page_dispose

Assigning a variable to itself when declaring it will result in it being
uninitialized.
Make sure to not mix free/g_free

In theory, they may not be using different allocator implementations.
Remove unused 'otherusage' variable
build-sys: Don't use deprecated INCLUDES

automake warns that it should be replaced by AM_CPPFLAGS. This commit
uses AM_CPPFLAGS for actual preprocessor directives, and AM_CFLAGS for
more generic CFLAGS (which could contain preprocessor directives
though).