Draw slope mode: by default slope vertices are now placed with the left mouse button, and drawing a slope is finished with the right mouse button

Stair sector builder: renamen "Single sectors" option to "Single steps". Added option to keep distinct sectors when using single steps

- 3D Floor Mode: fixed a bug where orphaned managed control sectors would be overwritten by relocating the control sectors

- 3D Floor Mode: removed non-functional "Spline" checkbox from the Edit Slope Vertex dialog

- Fixed a problem in the 3D floor mode plugin that caused an exception when saving the program preferences. Fixes #310.

- Flipped top/bottom in 3D Floor Mode plugin dialogs to be consistent with the edit sector dialog
@ fixed all compiler warnings in 3D Floor Mode plugin

- Fixed a bug where searching for generalized sector effects was not handled properly in Find & Replace Mode. Fixes 305.

- Auto-aligning textures now produces more intuitive results and is consistent between UDMF and non-UDMF maps

- Slope effects related to slope things are now displayed more correctly in visual mode (they were not applied at all). Fixes #160
- Slope effects of UDMF vertex heights are now displayed more correctly in visual mode (they could be overwritten by lower tier slopes)

- Unused textures error checker doesn't erroneously report textures on 3D floors with the use upper/lower flags set (followup to #269)
@ Refactored texture error checks to reuse code

- Added option to enable additive paint selecting without holding shift independently from regular additive selecting

- The missing textures checker now finds missing upper/lower textures on 3D floors when the appropriate flags of the Sector_Set3dFloor special are used. Fixes #269

- Textures will now wrap correctly in visual mode when the flag of the Line_SetIdentification special is set in Hexen format. Fixes #271

- Fixed a bug where the unknown texture error checker didn't report unknown textures on sidedefs that were never seen. Fixed #270

- Fixed a bug where moving the mouse outside the window could crash when pasting a selection while having auto dragging enabled. Fixes #110.

- Fixed a freeze in the Tag Range plug-in when using the "relative" and "skip used tags" options. Fixes #125.

- Improved support for auto aligning scaled textures