Implemented uiTabInsertPageBefore() on Windows.

TODO.md

@@ -71,3 +71,7 @@ notes to self
 - explicitly document label position at top-left corner
 - mark that uiControlShow() on a uiWindow() will bring to front and give keyboard focus because of OS X
 	- make sure ShowWindow() is sufficient for zorder on Windows
+- document that you can't use InsertBefore functions to insert before a nonexistent index (that includes if an array is empty)
+	- reconsider this, as the pointer array code does work with the first invalid index...
+		- we would need to test everything else with it
+- note that uiTabInsertPageBefore() does NOT change the current tab page (it may change its index if inserting before the current page)

test/page2.c

@@ -26,8 +26,9 @@ static void movePage1(uiButton *b, void *data)
 {
 	if (moveBack) {
 		uiBoxDelete(mainBox, 1);
-		uiTabInsertPageBefore(mainTab, 0, uiControl(page1));
+		uiTabInsertPageBefore(mainTab, "Page 1", 0, uiControl(page1));
 		uiButtonSetText(b, moveOutText);
+		moveBack = 0;
 		return;
 	}
 	uiTabDeletePage(mainTab, 0);

windows/tab.c

@@ -233,6 +233,32 @@ static void tabAppendPage(uiTab *tt, const char *name, uiControl *child)
 	SendMessageW(t->hwnd, msgUpdateChild, 0, 0);
 }
 
+static void tabInsertPageBefore(uiTab *tt, const char *name, uintmax_t n, uiControl *child)
+{
+	struct tab *t = (struct tab *) tt;
+	TCITEMW item;
+	struct tabPage *page;
+	WCHAR *wname;
+
+	page = uiNew(struct tabPage);
+
+	page->bin = newBin();
+	binSetMainControl(page->bin, child);
+	binSetParent(page->bin, (uintptr_t) (t->hwnd));
+	// always hide; the current tab doesn't change
+	uiControlHide(uiControl(page->bin));
+
+	ptrArrayInsertBefore(t->pages, n, page);
+
+	ZeroMemory(&item, sizeof (TCITEMW));
+	item.mask = TCIF_TEXT;
+	wname = toUTF16(name);
+	item.pszText = wname;
+	if (SendMessageW(t->hwnd, TCM_INSERTITEM, (WPARAM) n, (LPARAM) (&item)) == (LRESULT) -1)
+		logLastError("error adding tab to Tab in uiTabInsertPageBefore()");
+	uiFree(wname);
+}
+
 static void tabDeletePage(uiTab *tt, uintmax_t n)
 {
 	struct tab *t = (struct tab *) tt;
@@ -322,6 +348,7 @@ uiTab *uiNewTab(void)
 	uiControl(t)->SysFunc = tabSysFunc;
 
 	uiTab(t)->AppendPage = tabAppendPage;
+	uiTab(t)->InsertPageBefore = tabInsertPageBefore;
 	uiTab(t)->DeletePage = tabDeletePage;
 	uiTab(t)->NumPages = tabNumPages;
 	uiTab(t)->Margined = tabMargined;