Fail to build flow_manager examples when trema gem is used

[amotoki]

When trema is installed via "gem", a compilation of flow_manager examples fails with the following errors. flow_manager/examples/Makefile expects trema-config exists in ../../trema. It must check trema-config in the system using which.

make[1]: Entering directory /home/ubuntu/apps/flow_manager/examples' gcc -MM -std=gnu99 -D_GNU_SOURCE -g -fno-strict-aliasing -Werror -Wall -Wextra -Wformat=2 -Wcast-qual -Wcast-align -Wwrite-strings -Wconversion -Wfloat-equal -Wpointer-arith -I. -I.. utils.c example1.c example2.c example3.c example4.c example5.c > .depends ../libpath.h:26:19: fatal error: trema.h: No such file or directory compilation terminated. ../libpath.h:26:19: fatal error: trema.h: No such file or directory compilation terminated. ../libpath.h:26:19: fatal error: trema.h: No such file or directory compilation terminated. ../libpath.h:26:19: fatal error: trema.h: No such file or directory compilation terminated. ../libpath.h:26:19: fatal error: trema.h: No such file or directory compilation terminated. ../libpath.h:26:19: fatal error: trema.h: No such file or directory compilation terminated. make[1]: *** [depend] Error 1 make[1]: Leaving directory/home/ubuntu/apps/flow_manager/examples'
make: *** [examples] Error 2