Fixes related to external-json-parser (#165)
- configure: append conditionally json-parser to pc file
json-parser needs to be appended to Requires section of pkg-config file
when bitlbee is configured to use external-json-parser. This change is
needed for external plugins like bitlbee-steam.
- Makefile: do not install json.h when system json-parser is used
install-dev target should not install bundled json.h when bitlbee is
configured to use external-json-parser.
- Use correct json.h header file with respect to external_json_parser value
The preprocessor must include correct json.h header file with respect to
external_json_parser value, otherwise function prototypes and other
definitions do not need to correspond with object used for linking.
The state before this commit is that local version lib/json.h is used
always for compilation and external_json_parser variable controls if
local lib/json.o or global libjsonparser.so will be linked.
In order to fix this problem, #include directives in lib/json_util.h and
lib/oauth2.c were changed from "json.h" to <json.h> and preprocessor -I
flags were moved after conditional json-parser flags, which is enough
for solving the issue. Additionally, USE_EXTERNAL_JSON_PARSER macro is
exported when external-json-parser is used and it is used in lib/json.h
to trigger an error message, which should prevent similar mistakes in
future.
