Add an advanced pref to tweak the height of the underline cursor

sources/iTermAdvancedSettingsModel.h

@@ -180,5 +180,6 @@
 + (BOOL)useGCDUpdateTimer;
 + (BOOL)fullHeightCursor;
 + (BOOL)drawOutlineAroundCursor;
++ (double)underlineCursorOffset;
 @end

sources/iTermAdvancedSettingsModel.m

@@ -128,6 +128,7 @@ DEFINE_BOOL(focusReportingEnabled, YES, @"Terminal: Apps may turn on Focus Repor
 DEFINE_BOOL(useColorfgbgFallback, YES, @"Terminal: Use fallback for COLORFGBG if no exact match found?\nThe COLORFGBG variable indicates the ANSI colors that match the foreground and background colors. If no colors match and this setting is enabled, then the variable will be set to 15;0 to indicate a dark background or 0;15 to indicate a light background.");
 DEFINE_BOOL(zeroWidthSpaceAdvancesCursor, YES, @"Terminal: Zero-Width Space (U+200B) advances cursor?\nWhile a zero-width space should not advance the cursor per the Unicode spec, both Terminal.app and Konsole do this, and Weechat depends on it. You must restart iTerm2 after changing this setting.");
 DEFINE_BOOL(fullHeightCursor, NO, @"Terminal: Cursor occupies line spacing area.\nIf lines have more than 100% vertical spacing and this setting is enabled the bottom of the cursor will be aligned to the bottom of the spacing area.");
+DEFINE_FLOAT(underlineCursorOffset, 0, @"Terminal: Vertical offset for underline cursor.\nPositive values move it up, negative values move it down.");
 #pragma mark Hotkey
 DEFINE_FLOAT(hotkeyTermAnimationDuration, 0.25, @"Hotkey: Duration in seconds of the hotkey window animation.\nWarning: reducing this value may cause problems if you have multiple displays.");

sources/iTermCursor.m

@@ -76,7 +76,7 @@
              outline:(BOOL)outline {
     const CGFloat height = 2;
     NSRect cursorRect = NSMakeRect(rect.origin.x,
-                                   rect.origin.y + rect.size.height - height,
+                                   rect.origin.y + rect.size.height - height - [iTermAdvancedSettingsModel underlineCursorOffset],
                                    ceil(rect.size.width),
                                    height);
     if (outline) {