Moved checkpoints out of main, to prep for using them to help prevent DoS attacks

src/makefile.linux-mingw

@@ -32,6 +32,7 @@ CFLAGS=-O2 -w -Wno-invalid-offsetof -Wformat $(DEBUGFLAGS) $(DEFS) $(INCLUDEPATH
 HEADERS = \
     base58.h \
     bignum.h \
+    checkpoints.h \
     crypter.h \
     db.h \
     headers.h \
@@ -61,6 +62,7 @@ endif
 LIBS += -l mingwthrd -l kernel32 -l user32 -l gdi32 -l comdlg32 -l winspool -l winmm -l shell32 -l comctl32 -l ole32 -l oleaut32 -l uuid -l rpcrt4 -l advapi32 -l ws2_32 -l shlwapi
 
 OBJS= \
+    obj/checkpoints.o \
     obj/crypter.o \
     obj/db.o \
     obj/init.o \