(svn r13352) [0.6] -Backport from trunk (r13348, r13222, r13221, r13217):
- Fix: Industry tiles would sometimes tell they need a 'level' slope when they do not want the slope (r13348)
- Fix: Attempts to make the old AI perform better (r13217, r13221, r13222)

(svn r13351) -Codechange: disable warnings about unused variable for builds without asserts

(svn r13350) -Fix: wrong tooltip for waypoint picker scrollbar

(svn r13349) -Codechange: remove a pointless flag; the flag is set before calling a function and is then reset in the function without ever reading it. Patch by Cirdan.

(svn r13348) -Fix: an industry does not always need foundations; in the case of NewGRFs an industry can be built on a steep slope, however when 'querying' the foundation type of an industry we neglected the fact that these steep slope tiles do not have a foundation. As a result of this when one built a structure requiring foundations on a tile SW or SE of a steep slope industry tile it would try to apply the foundation on the steep slope to determine whether to draw the wall of the foundation and trigger an assert.

(svn r13347) -Fix (r12396): ottdres.rc.in was forgotten

(svn r13346) -Fix (r13322): scrolling the main viewport with keyboard when having a build tool selected failed.

(svn r13345) -Codechange: only one of all the NewsItem's instance duration variable, so move it so there is only once instance of that variable. Patch by Cirdan.

(svn r13344) -Codechange: remove some code duplication.

(svn r13343) -Codechange: reorder/move variable/functions in the network headers so that nothing from the network directory needs to include basically all network headers.