WB: fix recursive resolving dependet stimsets (e.g. formulas)

the algorithm in WB_StimsetChildren referenced the wrong column
of the WPT wave.
Fix: use the right stimset epoch type column (EPOCH_TYPE_COMBINE).

since introduction of dependent stimsets (EPOCH_TYPE_COMBINE)

Packages/MIES/MIES_WaveBuilder.ipf

@@ -2313,7 +2313,7 @@ static Function/S WB_StimsetChildren([stimset])
 	// search for stimsets in all formula-epochs by a regex pattern
 	for(i = 0; i < numEpochs; i += 1)
 		if(SegWvType[i] == 8)
-			formula = WPT[6][i][EPOCH_TYPE_CUSTOM]
+			formula = WPT[6][i][EPOCH_TYPE_COMBINE]
 			numStimsets = CountSubstrings(formula, "?")
 			for(j = 0; j < numStimsets; j += 1)
 				WAVE/T/Z wv = SearchStringBase(formula, "(.*)\\b(\\w+)\\b\\?(.*)")

Packages/tests/Basic/UTF_AnalysisBrowserTest.ipf

@@ -8,6 +8,7 @@
 
 static StrConstant PXP_FILENAME = "input:AB_LoadSweepsFromIgorData.pxp"
 static StrConstant PXP2_FILENAME = "input:AB_SweepsFromMultipleDevices.pxp"
+static StrConstant PXP3_FILENAME = "input:SourceOfDependentStimset.pxp"
 static StrConstant NWB1_FILENAME = "input:AB_SweepsFromMultipleDevices-compressed-V1.nwb"
 static StrConstant NWB2_FILENAME = "input:AB_SweepsFromMultipleDevices-compressed-V2.nwb"
 static StrConstant NWB3_FILENAME = ":_2017_09_01_192934-compressed.nwb"
@@ -152,3 +153,14 @@ static Function LoadStimsetsFromNWB()
 
 	KillWindow $abWin
 End
+
+static Function LoadDependentStimsetsFromPXP()
+
+	string abWin, sweepBrowsers, formulaSet
+
+	[abWin, sweepBrowsers] = OpenAnalysisBrowser({PXP3_FILENAME}, loadStimsets = 1)
+	formulaSet = MIES_WB#WB_StimsetChildren(stimset="baseset_DA_0")
+	CHECK_EQUAL_STR(formulaSet, "formula_da_0;")
+
+	KillWindow $abWin
+End