Optimization for case when alpha is zero.

git-svn-id: svn://svn.code.sf.net/p/agg/svn/agg-2.4@95 ab9de31f-a152-4fe9-8809-95f286f9ca89
Added missing conversions for gray16->rgba32 and gray32->rgba32.

git-svn-id: svn://svn.code.sf.net/p/agg/svn/agg-2.4@96 ab9de31f-a152-4fe9-8809-95f286f9ca89
Added missing "plain" pixel formats.

git-svn-id: svn://svn.code.sf.net/p/agg/svn/agg-2.4@97 ab9de31f-a152-4fe9-8809-95f286f9ca89
Fixed a typo and compiler warnings about conversion from double to float.

git-svn-id: svn://svn.code.sf.net/p/agg/svn/agg-2.4@98 ab9de31f-a152-4fe9-8809-95f286f9ca89
Removed "Step" and "Offset" template parameters of gray/rgb pixel formats. Instead, the component order and pixel size is now fully specified by "order_type".

git-svn-id: svn://svn.code.sf.net/p/agg/svn/agg-2.4@99 ab9de31f-a152-4fe9-8809-95f286f9ca89
Avoid potential compiler warning about converting double to float.

git-svn-id: svn://svn.code.sf.net/p/agg/svn/agg-2.4@100 ab9de31f-a152-4fe9-8809-95f286f9ca89
Added "explicit" specifier to constructors that would otherwise allow undesirable implicit conversion from integer types.

git-svn-id: svn://svn.code.sf.net/p/agg/svn/agg-2.4@101 ab9de31f-a152-4fe9-8809-95f286f9ca89