In compiling release version, add flag "-g" for debug info.
As ijma contains iconv source code, if the user code also calls "iconv" function from libc,
it might link to ijma's "iconv" definition incorrectly, at runtime, segment fault might
happen.

In order to fix this problem, in ijma, the macro "LIBICONV_PLUG" is undefined, so that
the function "iconv" would be renamed to "libiconv", and user code could link to libc's
"iconv" definition.
Merge branch 'master' of https://github.com/izenecloud/ijma