Add Travis-CI build job

[tresf]

A proposal to enable continuous builds through Travis-CI, which can be extended to do a few neat (and perhaps obvious) things...

• Can be used to flag on Homebrew/Mac builds using XCode/Clang (not in this PR)
• Can be used to upload ELF build artifacts for precompiled binaries (not in this PR)

Note:

• Enabling this requires visiting travis-ci.org and clicking the "Enable" checkbox next to swh/ladspa.
• This PR contains 3 additional commits not yet approved in mainline.

A successful build is here: https://travis-ci.org/tresf/ladspa/builds/296613052. Sample output:

Found 96 files
-------
alias_1407.so			karaoke_1409.so
allpass_1895.so			latency_1914.so
amp_1181.so			lcr_delay_1436.so
am_pitchshift_1433.so		lowpass_iir_1891.so
analogue_osc_1416.so		ls_filter_1908.so
bandpass_a_iir_1893.so		matrix_ms_st_1421.so
bandpass_iir_1892.so		matrix_spatialiser_1422.so
bode_shifter_1431.so		matrix_st_ms_1420.so
bode_shifter_cv_1432.so		mbeq_1197.so
butterworth_1902.so		mod_delay_1419.so
chebstortion_1430.so		multivoice_chorus_1201.so
comb_1190.so			notch_iir_1894.so
comb_1887.so			phasers_1217.so
comb_splitter_1411.so		pitch_scale_1193.so
const_1909.so			pitch_scale_1194.so
crossover_dist_1404.so		plate_1423.so
dc_remove_1207.so		pointer_cast_1910.so
decay_1886.so			rate_shifter_1417.so
decimator_1202.so		retro_flange_1208.so
declip_1195.so			revdelay_1605.so
delay_1898.so			ringmod_1188.so
delayorama_1402.so		satan_maximiser_1408.so
diode_1185.so			sc1_1425.so
divider_1186.so			sc2_1426.so
dj_eq_1901.so			sc3_1427.so
dj_flanger_1438.so		sc4_1882.so
dyson_compress_1403.so		sc4m_1916.so
fad_delay_1192.so		se4_1883.so
fast_lookahead_limiter_1913.so	shaper_1187.so
flanger_1191.so			sifter_1210.so
fm_osc_1415.so			sin_cos_1881.so
foldover_1213.so		single_para_1203.so
foverdrive_1196.so		sinus_wavewrapper_1198.so
freq_tracker_1418.so		smooth_decimate_1414.so
gate_1410.so			split_1406.so
giant_flange_1437.so		step_muxer_1212.so
gong_1424.so			surround_encoder_1401.so
gong_beater_1439.so		svf_1214.so
gsm_1215.so			tape_delay_1211.so
gverb_1216.so			transient_1206.so
hard_limiter_1413.so		triple_para_1204.so
harmonic_gen_1220.so		valve_1209.so
hermes_filter_1200.so		valve_rect_1405.so
highpass_iir_1890.so		vocoder_1337.so
hilbert_1440.so			vynil_1905.so
imp_1199.so			wave_terrain_1412.so
impulse_1885.so			xfade_1915.so
inv_1429.so			zm1_1428.so