Graphs: use chars to store line number

This reduces memory cost somewhat (10MB on the git.git repository),
while still keeping the same functionality :) Better would be to
use structs in a c array in the cellinfo, as the NSArray and
NSObject type information together now use more memory.

PBGitGraphLine.h

@@ -11,14 +11,14 @@
 
 @interface PBGitGraphLine : NSObject
 {
-	int upper;
-	int from;
-	int to;
-	int colorIndex;
+	char upper;
+	char from;
+	char to;
+	char colorIndex;
 }
-@property(readonly) int upper, from, to, colorIndex;
-- (id)initWithUpper: (int) u From: (int) f to: (int) t color: (int) c;
-+ (PBGitGraphLine*) lowerLineFrom:(int) f to: (int) t color: (int) c;
-+ (PBGitGraphLine*) upperLineFrom:(int) f to: (int) t color: (int) c;
+@property(readonly) char upper, from, to, colorIndex;
+- (id)initWithUpper: (char) u From: (char) f to: (char) t color: (char) c;
++ (PBGitGraphLine*) lowerLineFrom:(char) f to: (char) t color: (char) c;
++ (PBGitGraphLine*) upperLineFrom:(char) f to: (char) t color: (char) c;
 
 @end

PBGitGraphLine.m

@@ -11,7 +11,7 @@
 
 @implementation PBGitGraphLine
 @synthesize upper, from, to, colorIndex;
-- (id)initWithUpper: (int) u From: (int) f to: (int) t  color: (int) c;
+- (id)initWithUpper: (char) u From: (char) f to: (char) t  color: (char) c;
 {
 	upper = u;
 	from = f;
@@ -20,12 +20,12 @@
 	return self;
 }
 
-+ (PBGitGraphLine*) lowerLineFrom:(int) f to: (int) t color: (int) c
++ (PBGitGraphLine*) lowerLineFrom:(char) f to: (char) t color: (char) c
 {
 	return [[PBGitGraphLine alloc] initWithUpper:0 From:f to:t color:c];
 }
 
-+ (PBGitGraphLine*) upperLineFrom:(int) f to: (int) t color: (int) c
++ (PBGitGraphLine*) upperLineFrom:(char) f to: (char) t color: (char) c
 {
 	return [[PBGitGraphLine alloc] initWithUpper:1 From:f to:t color: c];
 }