Add . to the include search path

Look for headers in . as well, just to make sure it works for those
having minisat-includes saved in the project directory.

Makefile

@@ -29,7 +29,7 @@ PROGS := coalg coalgcompare
 LIBS := unix str
 SOURCESMLI := $(wildcard *.mli)
 SOURCESML := $(wildcard *.ml)
-INCS ?= -I/usr/include -I/usr/lib/ocaml
+INCS ?= -I/usr/include -I/usr/lib/ocaml -I.
 CXXFLAGS += -Wall -Werror $(INCS)
 LDXX ?= g++