Merge branch 'master' into amber-switching

 Conflicts:
	wrappers/python/simtk/openmm/app/amberprmtopfile.py

In fixing the merge conflict, I went ahead and fixed up the switchDistance logic
to match what I did in CharmmPsfFile.

wrappers/python/tests/systems/alanine-dipeptide-amoeba-forces.xml

+<?xml version="1.0" ?>
+<State time="0" type="State" version="1">
+	<PeriodicBoxVectors>
+		<A x="2" y="0" z="0"/>
+		<B x="0" y="2" z="0"/>
+		<C x="0" y="0" z="2"/>
+	</PeriodicBoxVectors>
+	<Forces>
+		<Force x="-60.899006905648534" y="-704.8991281062977" z=".0364180169671772"/>
+		<Force x="1179.7263311404506" y="629.2168542831286" z="1.563821009034657"/>
+		<Force x="-484.4401097634541" y="135.94210610096957" z="558.0155391926069"/>
+		<Force x="-484.1625627429897" y="136.02915381525668" z="-557.7203977673528"/>
+		<Force x="-804.8403408476064" y="-857.579131840898" z="118.43755474210333"/>
+		<Force x="84.24441920455223" y="-421.86322192608037" z="120.734742628977"/>
+		<Force x="666.4942549112259" y="-479.03339298154526" z="19.66166555862896"/>
+		<Force x="-518.9062723002917" y="686.3850843706331" z=".7311137123231983"/>
+		<Force x="-105.62094199225953" y="710.9845370176521" z="-508.0677463920413"/>
+		<Force x="285.6690654282444" y="-111.35548608152155" z="847.8096733172159"/>
+		<Force x="-396.4822698774795" y="24.462223992557014" z="297.9581483103431"/>
+		<Force x="-168.22340166944585" y="110.99779797739818" z="-824.0916382722021"/>
+		<Force x="805.7023041833917" y="15.738288953519556" z="-340.2263402925698"/>
+		<Force x="366.3025998383222" y="-647.7535895818237" z="-273.83047817845636"/>
+		<Force x="-649.7310636705703" y="-495.52797252280067" z="317.36013856851315"/>
+		<Force x="-480.120788018345" y="172.44477988154952" z="-16.235455767965004"/>
+		<Force x="-486.20230228601736" y="982.6376366390087" z="127.20818643942287"/>
+		<Force x="820.5730252078641" y="-78.71234329038225" z="109.31395566365498"/>
+		<Force x="355.03388135028814" y="-1391.2776654673507" z=".9942543092954484"/>
+		<Force x="-511.3467906691061" y="677.7717086552518" z=".008253291392112616"/>
+		<Force x="293.66157422204157" y="452.68343054060256" z="502.83463917630775"/>
+		<Force x="293.5683952568295" y="452.70832957117113" z="-502.49604726620026"/>
+	</Forces>
+</State>