Show more compiler warnings

[ltog]

In #61 we have a case of an uninitialized variable. This was not reported by compilers. Maybe we can adjust the Makefile to get more warnings?

[ltog]

First of all: g++ (and clang++) has the option -Wall but that doesn't enable all warnings...

clang++ has the option

-Weverything

which is supposed to really warn about everything. See http://clang.llvm.org/docs/UsersManual.html#diagnostics-enable-everything

To filter out some irrelevant warnings after using -Weverything, we can append:

-Wno-c++98-compat -Wno-c++98-compat-pedantic

[ltog]

-Weverything is ok, but provokes warnings from the GDAL library.

Some ideas to suppress those:

• https://stackoverflow.com/questions/1305665/how-to-compile-different-c-files-with-different-cflags-using-makefile
• https://stackoverflow.com/questions/1867065/how-to-suppress-gcc-warnings-from-library-headers

[ltog]

More warnings from g++:

• https://stackoverflow.com/questions/5088460/flags-to-enable-thorough-and-verbose-g-warnings
• https://stackoverflow.com/questions/11714827/how-to-turn-on-literally-all-of-gccs-warnings