change handling of embedded version information

rather than modifying push.cpp as part of the built process, this
passes in a version string on the command.  This is a little cleaner
(it does not lead to false changes in push.cpp) and makes it easier for a
packager to provide explicit version information, e.g., by passing in
version information to make:

    make version=`lars-test'

Makefile

@@ -1,4 +1,4 @@
-version := $(shell git describe --dirty)
+version = $(shell git describe --dirty || echo dev)
 curl=no
 
 ifneq ($(curl),no)
@@ -7,10 +7,11 @@ else
 	flags=
 endif
 
+all: push.so
+
 push.so: push.cpp
-	sed -i "" -e "s|PUSHVERSION \".*\"|PUSHVERSION \"$(version)\"|" push.cpp
-	CXXFLAGS="$(CXXFLAGS) $(flags)" LIBS="$(LIBS) $(flags)" znc-buildmod push.cpp
-	sed -i "" -e "s|PUSHVERSION \".*\"|PUSHVERSION \"dev\"|" push.cpp
+	CXXFLAGS="$(CXXFLAGS) -DPUSHVERSION=\"$(version)\" $(flags)" LIBS="$(LIBS) $(flags)" \
+		 znc-buildmod push.cpp
 
 install: push.so
 	mkdir -p $(HOME)/.znc/modules/

push.cpp

@@ -9,7 +9,9 @@
  */
 
 #define REQUIRESSL
+#ifndef PUSHVERSION
 #define PUSHVERSION "dev"
+#endif
 
 #include <znc/znc.h>
 #include <znc/Chan.h>