move wallet code to separate file

This introduces two new source files, keystore.cpp and wallet.cpp with
corresponding headers. Code is moved from main and db, in a preparation
for a follow-up commit which introduces the classes CWallet and CKeyStore.

src/makefile.unix

@@ -39,7 +39,7 @@ LIBS+= \
 DEBUGFLAGS=-g -D__WXDEBUG__
 CXXFLAGS=-O2 -Wno-invalid-offsetof -Wformat $(DEBUGFLAGS) $(DEFS)
 HEADERS=headers.h strlcpy.h serialize.h uint256.h util.h key.h bignum.h base58.h \
-    script.h db.h net.h irc.h main.h rpc.h uibase.h ui.h noui.h init.h
+    script.h db.h net.h irc.h keystore.h main.h wallet.h rpc.h uibase.h ui.h noui.h init.h
 
 OBJS= \
     obj/util.o \
@@ -47,7 +47,9 @@ OBJS= \
     obj/db.o \
     obj/net.o \
     obj/irc.o \
+    obj/keystore.o \
     obj/main.o \
+    obj/wallet.o \
     obj/rpc.o \
     obj/init.o \
     cryptopp/obj/sha.o \