make qmake build system more configurable (as suggested by lukejr)

bitcoin-qt.pro

@@ -5,7 +5,12 @@ DEFINES += QT_GUI
 # DEFINES += SSL
 CONFIG += no_include_pwd
 
-LIBS += -lssl -lcrypto -ldb_cxx
+# for boost 1.37, add -mt to the boost libraries 
+# use: qmake BOOST_LIB_SUFFIX=-mt
+
+# Dependency library locations can be customized with BOOST_INCLUDE_PATH, 
+#    BOOST_LIB_PATH, BDB_INCLUDE_PATH, BDB_LIB_PATH
+#    OPENSSL_INCLUDE_PATH and OPENSSL_LIB_PATH respectively
 
 # use: qmake "USE_UPNP=1"
 # miniupnpc (http://miniupnp.free.fr/files/) must be installed
@@ -170,19 +175,38 @@ TRANSLATIONS = src/qt/locale/bitcoin_nl.ts src/qt/locale/bitcoin_de.ts \
 OTHER_FILES += \
     README.rst
 
-# Platform-specific libraries/includes
-# for boost 1.37, add -mt to the boost libraries
-unix:!macx:LIBS += -lboost_system -lboost_filesystem -lboost_program_options -lboost_thread
-macx:LIBS += -lboost_system-mt -lboost_filesystem-mt -lboost_program_options-mt -lboost_thread-mt
-macx:DEFINES += __WXMAC_OSX__ MSG_NOSIGNAL=0 BOOST_FILESYSTEM_VERSION=3
-windows:LIBS += -lboost_system-mgw44-mt-1_43 -lboost_filesystem-mgw44-mt-1_43 -lboost_program_options-mgw44-mt-1_43 -lboost_thread-mgw44-mt-1_43 -lws2_32 -lgdi32
+# platform specific defaults, if not overridden on command line
+isEmpty(BOOST_LIB_SUFFIX) {
+    macx:BOOST_LIB_SUFFIX = -mt
+    windows:BOOST_LIB_SUFFIX = -mgw44-mt-1_43
+}
+
+isEmpty(BDB_LIB_PATH) {
+    macx:BDB_LIB_PATH = /opt/local/lib/db48
+}
+
+isEmpty(BDB_INCLUDE_PATH) {
+    macx:BDB_INCLUDE_PATH = /opt/local/include/db48
+}
+
+isEmpty(BOOST_LIB_PATH) {
+    macx:BOOST_LIB_PATH = /opt/local/lib
+}
+
+isEmpty(BOOST_INCLUDE_PATH) {
+    macx:BOOST_INCLUDE_PATH = /opt/local/include
+}
+
+windows:LIBS += -lws2_32 -lgdi32
 windows:DEFINES += __WXMSW__
 windows:RC_FILE = src/qt/res/bitcoin-qt.rc
 
-# For use with MacPorts
-macx:INCLUDEPATH += /opt/local/include /opt/local/include/db48
-macx:LIBS += -L/opt/local/lib -L/opt/local/lib/db48
-
-# Additional Mac options
+macx:DEFINES += __WXMAC_OSX__ MSG_NOSIGNAL=0 BOOST_FILESYSTEM_VERSION=3
 macx:ICON = src/qt/res/icons/bitcoin.icns
 macx:TARGET = "Bitcoin Qt"
+
+# Set libraries and includes at end, to use platform-defined defaults if not overridden
+INCLUDEPATH += $$BOOST_INCLUDE_PATH $$BDB_INCLUDE_PATH $$OPENSSL_INCLUDE_PATH
+LIBS += $$join(BOOST_LIB_PATH,,-L,) $$join(BDB_LIB_PATH,,-L,) $$join(OPENSSL_LIB_PATH,,-L,)
+LIBS += -lssl -lcrypto -ldb_cxx
+LIBS += -lboost_system$$BOOST_LIB_SUFFIX -lboost_filesystem$$BOOST_LIB_SUFFIX -lboost_program_options$$BOOST_LIB_SUFFIX -lboost_thread$$BOOST_LIB_SUFFIX